Guidance on Waterborne Bacterial Pathogens

Guidance on Waterborne Bacterial Pathogens
Guidance on
Waterborne Bacterial Pathogens
Document for Public Comment
Prepared by the Federal-Provincial-Territorial
Committee on Drinking Water
Consultation period ends
September 21, 2012
Guidance on waterborne bacterial pathogens
For Public Consultation
Guidance on Waterborne Bacterial Pathogens
Document for Public Consultation
Table of Contents
Purpose of consultation .................................................................................................................. 1
Background on guidance documents ............................................................................................ 2
Part A. Guidance on waterborne bacterial pathogens................................................................ 3
Part B. Supporting information .................................................................................................... 5
B.1
Enteric waterborne pathogens .......................................................................................... 5
B.1.1 Pathogenic Escherichia coli ..................................................................................... 5
B.1.1.1 Treatment technology ............................................................................... 6
B.1.1.2 Assessment ............................................................................................... 6
B.1.2 Salmonella and Shigella ........................................................................................... 7
B.1.2.1 Treatment technology ............................................................................... 8
B.1.2.2 Assessment ............................................................................................... 8
B.1.3 Campylobacter and Yersinia .................................................................................... 8
B.1.3.1 Treatment technology ............................................................................... 9
B.1.3.2 Assessment ............................................................................................... 9
B.2
Other bacterial pathogens ................................................................................................. 9
B.2.1 Legionella ................................................................................................................. 9
B.2.1.1 Sources and exposure ............................................................................... 9
B.2.1.2 Health effects .......................................................................................... 11
B.2.1.3 Treatment technology ............................................................................. 12
B.2.1.4 Assessment ............................................................................................. 13
B.2.2 Mycobacterium avium complex ............................................................................. 14
B.2.2.1 Sources and exposure ............................................................................. 14
B.2.2.2 Health effects .......................................................................................... 16
B.2.2.3 Treatment technology ............................................................................. 16
B.2.2.4 Assessment ............................................................................................. 18
B.2.3 Aeromonas .............................................................................................................. 18
B.2.3.1 Sources and exposure ............................................................................. 18
B.2.3.2 Health effects .......................................................................................... 20
B.2.3.3 Treatment technology ............................................................................. 22
B.2.3.4 Assessment ............................................................................................. 23
B.2.4 Helicobacter pylori ................................................................................................ 24
B.2.4.1 Sources and exposure ............................................................................. 24
B.2.4.2 Health effects .......................................................................................... 25
B.2.4.3 Treatment technology ............................................................................. 25
B.2.4.4 Assessment ............................................................................................. 26
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Guidance on waterborne bacterial pathogens
B.3.
For Public Consultation
Issues of Emerging Interest ............................................................................................. 27
B.3.1. Disinfection and antibiotic resistance in organisms ............................................... 27
B.3.2. Residential-scale and private drinking water systems............................................ 27
B.3.3. Point of entry and point of use treatment devices. ................................................. 28
Part C. References and acronyms ............................................................................................... 30
C.1
References ......................................................................................................................... 30
C.2
List of acronyms ............................................................................................................... 53
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Guidance on waterborne bacterial pathogens
For Public Consultation
July 2012
Guidance on Waterborne Bacterial Pathogens
Purpose of consultation
The Federal-Provincial-Territorial Committee on Drinking Water (CDW) has assessed the
available information on waterborne bacterial pathogens with the intent of establishing a drinking
water guidance document. The purpose of this consultation is to solicit comments on this
guidance document.
The CDW has requested that this document be made available to the public and open for
comment. Comments are appreciated, with accompanying rationale, where required. Comments
can be sent to the CDW Secretariat via email at [email protected] If this is not feasible,
comments may be sent by mail to the CDW Secretariat, Water, Air and Climate Change Bureau,
Health Canada, 3rd Floor, 269 Laurier Avenue West, A.L. 4903D, Ottawa, Ontario K1A 0K9.
All comments must be received before September 21, 2012.
It should be noted that this Guidance Document on Waterborne Bacterial pathogens will
be revised following evaluation of comments received, and a final guidance document will be posted. This
document should be considered as a draft for comment only.
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Guidance on waterborne bacterial pathogens
For Public Consultation
Guidance on waterborne bacterial pathogens
Background on guidance documents
The main role of the Federal-Provincial-Territorial Committee on Drinking Water is the
development of the Guidelines for Canadian Drinking Water Quality. This role has evolved over
the years, and new methodologies and approaches have led the Committee to develop a new type
of document, Guidance documents, to provide advice and guidance on issues related to drinking
water quality for parameters that do not require a formal Guideline for Canadian Drinking Water
Quality.
There are two instances when the Federal-Provincial-Territorial Committee on Drinking
Water may choose to develop guidance documents. The first would be to provide operational or
management guidance related to specific drinking water related issues (such as boil water
advisories), in which case the documents would provide only limited scientific information or
health risk assessment. The second instance would be to make risk assessment information
available when a guideline is not deemed necessary.
The Federal-Provincial-Territorial Committee on Drinking Water establishes the
Guidelines for Canadian Drinking Water Quality specifically for contaminants that meet all of the
following criteria:
1. exposure to the contaminant could lead to adverse health effects;
2. the contaminant is frequently detected or could be expected to be found in a large number
of drinking water supplies throughout Canada; and
3. the contaminant is detected, or could be expected to be detected, at a level that is of
possible health significance.
If a contaminant of interest does not meet all these criteria, the Federal-ProvincialTerritorial Committee on Drinking Water may choose not to establish a numerical guideline or
develop a Guideline Technical Document. In that case, a guidance document may be developed.
Guidance documents undergo a similar process as Guideline Technical Documents,
including public consultations through the Health Canada web site. They are offered as
information for drinking water authorities, and in some cases to help provide guidance in spill or
other emergency situations.
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Guidance on waterborne bacterial pathogens
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July 2012
Part A. Guidance on waterborne bacterial pathogens
Throughout history, consumption of drinking water supplies of poor sanitary quality has
been linked to illnesses in human populations. These illnesses most commonly present as
gastrointestinal-related symptoms, such as diarrhoea and nausea. The organisms identified within
this document as enteric waterborne bacterial pathogens are those that have been well-established
as having a history of being responsible for waterborne outbreaks of gastrointestinal illness.
Although there are methods capable of detecting and measuring pathogenic bacteria in drinking
water, routine monitoring for these organisms still remains difficult and impractical. This is
because there are a number of types of bacterial pathogens that can be present in human and/or
animal wastes that can vary significantly in their distribution depending on the sources of
contamination impacting the water supply; and conducting detection and identification
procedures for each possible type can be difficult, requiring significant resources. As a result,
monitoring for a broad indicator of fecal contamination such as E. coli is useful in verifying the
microbiological water quality and safety of the drinking water supply. Detection of elevated
numbers of E. coli is indicative of fecal contamination and thus indicates that enteric bacterial
pathogens may possibly be present.
In recent decades, there has been an increasing amount of interest in waterborne bacterial
pathogens that occur naturally in the water environment and thus have the potential to be
transmitted through water. These other waterborne bacterial pathogens discussed within this
document can cause human infection resulting in gastrointestinal and non-gastrointestinal
illnesses (particularly respiratory illnesses). Routine monitoring for these pathogens remains
impractical as well. As these organisms occupy different environmental niches and have primary
sources other than human or animal faeces, there are presently no satisfactory microbiological
indicators for their presence. To date, none of these organisms have been associated with
outbreaks of illness as a result of exposure to drinking water supplies in Canada. However, as
they do have the potential to be spread through drinking water, it is important to ensure that the
treatment and disinfection strategies in place are capable of providing adequate control of these
organisms.
Health Canada maintains that the best means of safeguarding against the presence of
waterborne pathogens (including non-faecal pathogens) in drinking water is the application of the
multi-barrier approach that includes adequate treatment, a well-maintained distribution system,
and, in the case of enteric bacteria - source protection. Treatment and disinfection requirements in
the provision of microbiologically safe drinking water are based on health-based treatment goals
for the removal and inactivation of the enteric protozoa Giardia and Cryptosporidium and enteric
viruses. These organisms present a significant challenge to water treatment and disinfection
technologies because of their difficulty of removal, high infectivity and high disinfectant
resistance. As a result, current drinking water treatment and disinfection practices applied to meet
the treatment goals for viruses and protozoa are expected to be similarly capable of controlling
waterborne bacterial pathogens in drinking water. This approach can reduce both faecal and nonfaecal pathogens to non-detectable levels or to levels that have not been associated with human
illness.
Consequently, it remains unnecessary and impractical to establish maximum acceptable
concentrations for the waterborne bacterial pathogens described in this document. The
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Guidance on waterborne bacterial pathogens
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monitoring of indicators such as E. coli continues to be used in the verification of the
microbiological quality of drinking water.
Under the multi-barrier approach to safe drinking water, numerous process controls are
required to function alongside bacteriological analysis in order to reliably produce drinking water
of an acceptable quality. Important individual elements under this approach include:
• source water protection (where possible);
• optimized treatment performance (e.g., for turbidity reduction and particle removal);
• proper application of disinfection technologies;
• a well-designed and maintained distribution system; and
• maintenance of a disinfection residual.
The potential for introduction of waterborne bacterial pathogens into the distribution
system and the capability for survival and regrowth in biofilms are of concern in drinking water
treatment. Additional considerations specific for aiding in the control of biofilms in the
distribution system can include:
• use of proper construction materials;
• control measures to reduce levels of natural organic matter, scaling and corrosion;
• measures to prevent low flow rates or water stagnation and to control temperatures (where
possible); and
• maintenance activities such as flushing and cleaning.
Contamination problems involving waterborne bacterial pathogens can occur in water
systems outside of water treatment plants’ distribution network, such as plumbing systems, or
heating, ventilation and air conditioning systems. Specific information pertaining to guidance and
requirements for these systems can be found by consulting the proper regulatory authority.
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Guidance on waterborne bacterial pathogens
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Part B. Supporting information
B.1
Enteric waterborne pathogens
B.1.1 Pathogenic Escherichia coli
Escherichia coli are bacteria found naturally in the digestive tract of warm-blooded
animals, including humans. As such, it is used in the drinking water industry as the definitive
indicator of recent faecal contamination of water. While most strains of E. coli are nonpathogenic, some possess virulence traits that can enable them to cause serious diarrhoeal
infections in humans. These pathogenic E. coli are divided into groups based on the mechanisms
with which they interact with human intestinal tract and cause symptoms (e.g., produce specific
types of toxin; or invade, bind to, or cause structural alterations of intestinal cells) (Percival et al.,
2004). The six groups are: enterohaemorrhagic (EHEC), enterotoxigenic (ETEC), enteroinvasive
(EIEC), enteropathogenic (EPEC), enteroaggregative (EAEC), and diffuse adherent (DAEC) E.
coli (Percival et al., 2004; AWWA, 2006). The EHEC group has emerged as a group that is of
particular significance to the water industry (AWWA, 2006). This group is a broad group which
contains many different serotypes that have been implicated as causes of human illness (Muniesa
et al., 2006). One member of the EHEC group E. coli O157:H7, has been most commonly
associated with pathogenic E. coli outbreaks worldwide (Muniesa et al., 2006) and has been
implicated in a few waterborne outbreaks (Bruce-Grey-Owen Sound Health Unit, 2000; Schuster
et al., 2005; Craun et al., 2006; Clark et al., 2010). In Canada, the Walkerton outbreak of 2000
was the first documented outbreak of Escherichia coli O157:H7 infection associated with a
Canadian municipal water supply and the largest multiwaterborne bacterial outbreak in the
country to date (Bruce-Grey-Owen Sound Health Unit, 2000). Surveillance reports published for
other countries have indicated that over the period from 1990 to the early 2000’s, E. coli
O157:H7 has been identified as the causative agent of approximately 6% of the reported drinking
water outbreaks in England and Wales (Smith et al., 2006) and roughly 7% of those reported in
the United States (Craun et al., 2006).
Cattle and human sewage are the primary and secondary sources, respectively, of EHEC
(Jackson et al., 1998; Percival et al., 2004). Human sewage is the major source of the other
pathogenic E. coli groups (Percival et al., 2004; AWWA, 2006). Transmission of pathogenic E.
coli occurs through the fecal-oral route, and the primary routes of exposure are from
contaminated food, water or from person to person (Percival et al., 2004, AWWA, 2006).
Pathogenic E. coli are not usually a concern in treated drinking water, however outbreaks of E.
coli O157:H7 involving consumption of drinking water contaminated with human sewage or
cattle faeces have been documented (Swerdlow et al., 1992; Bruce-Grey-Owen Sound Health
Unit, 2000).
The probability of becoming ill depends on the number of organisms ingested, the health
status of the person, and the resistance of the person to the organism or toxin (AWWA, 1999).
With the exception of EHEC, most pathogenic E. coli require a high number of bacteria to
be ingested in order to produce illness. Infectious dose estimates for non-EHEC strains range
from 105 to 1010 organisms (Percival et al., 2004). EHEC strains on the other hand have a very
low infectious dose. It has been suggested that ingestion of fewer than 100 cells may be sufficient
to cause infection (Percival et al., 2004, Pond, 2005). The onset and duration of pathogenic E.
coli related illness will be strain dependent, but symptoms can begin in as little as 8-12 hours and
last from a few days to up to a few weeks (Percival et al., 2004).
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Pathogenic E. coli can cause diarrhoea that ranges in severity from mild and self-limiting
to severe and life-threatening (Percival et al., 2004; AWWA, 2006). Most non-EHEC illness is
marked by a watery diarrhoea that can be accompanied by vomiting, abdominal pain, fever and
muscle pain depending on the group or strain involved.
EHEC illness can begin with watery and bloody diarrhoea in combination with vomiting,
but in some cases can progress to the more serious and potentially life-threatening symptoms of
hemorrhagic colitis (grossly bloody diarrhoea) and haemolytic uremic syndrome (kidney failure).
These symptoms are caused by shiga-like toxins, potent toxins that are related to Shigella
dysenteriae toxins (Percival et al., 2004). It has been proposed that up to 10% of E. coli O157:H7
infections can progress to haemolytic uremic syndrome (Moe, 1997; Sherman et al., 2010).
Children and the elderly are most susceptible to the complications that arise from EHEC
infections (Percival et al., 2004). One area of recent study interest has been the examination of
possible long-term health effects in adults as a result of contracting haemolytic uremic syndrome
from E. coli O157:H7, as these to date have been largely unknown (Clark et al., 2010). Clark et
al. (2010) reported on the results of a health study among persons exposed and unexposed to
gastrointestinal illness from E. coli O157:H7 and Campylobacter during the Walkerton outbreak
in May 2000. The author’s conclusions were that the data provided evidence of increases in the
incidence of hypertension, cardiovascular disease and indicators of kidney impairment in persons
who experienced acute gastroenteritis during the outbreak. Further study in this area is required.
B.1.1.1 Treatment technology
In the majority of treatment and disinfection studies involving pathogenic E. coli it is the
EHEC strain O157:H7 that has been selected as the model organism due to its health significance
and prominence in foodborne and waterborne outbreaks. Regardless, review of the evidence
generated to date suggests that the proper application of water treatment and disinfection
technologies will be capable of controlling strains of pathogenic and non-pathogenic E. coli in
drinking water (Percival et al., 2004; AWWA, 2006).
In terms of chlorine and monochloramine effectiveness, laboratory studies have
demonstrated E. coli O157:H7 log inactivation capabilities of up to 4 log at concentrations and
contact times that would be encountered in municipal drinking water treatment (Rice et al., 1999;
Wojcicka et al., 2007; Chauret et al., 2008).
For UV disinfection, Zimmer-Thomas et al. (2007) observed log inactivations of 4.5 log
or greater for E. coli O157:H7 at all tested doses of low pressure (LP) and medium pressure (MP)
UV. These included UV doses commonly used in water disinfection (20 and 40 mJ/cm2, LP), as
well as low doses intended to be representative of compromised UV dose delivery (5 and
8 mJ/cm2, LP and MP). In UV inactivation experiments, Sommer et al. (2000) observed
considerable divergence in sensitivity of different pathogenic (including enterohemorrhagic)
strains of E. coli. The authors further demonstrated that a UV dose of 125 J/m2 (equivalent to
12.5 mJ/cm2) was sufficient to produce a 6-log inactivation of all of the strains under study.
Further information on treatment technology for E. coli can be found in the Escherichia coli
guideline technical document (Health Canada, 2012).
B.1.1.2 Assessment
Studies have shown that the survival and susceptibility to disinfection of pathogenic E.
coli strains approximates that of typical E. coli (AWWA, 1999; Rice, 1999). Also, although
routine examination methods for generic E. coli are not designed to distinguish pathogenic E. coli
strains, the former will always occur in greater concentration in faeces, even during outbreaks.
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Pathogenic E. coli will not occur in the absence of generic E. coli. As a result, the presence of E.
coli can be used as an indicator of the presence of pathogenic E. coli.
B.1.2 Salmonella and Shigella
Salmonella and Shigella are agents of gastrointestinal illness that belong to the same
microbiological family as E. coli.
Salmonella is a complex taxonomic genus consisting of over 2000 different varieties or
serological types that can cause infections in animals and humans (AWWA, 2006). According to
experts, the genus is officially made up of only two species, Salmonella enterica and Salmonella
bongori (Percival et al., 2004, AWWA, 2006). Salmonella enterica is the species of most
relevance for human infections and it can be further broken down into 6 subspecies, of which
one, Salmonella enterica subspecies enterica contains the majority of serotypes that are
associated with cases of human gastroenteritis (Percival et al., 2004). By convention, when
referring to Salmonella serotypes, the serotype is adopted as the species name (for example:
Salmonella enterica subsp. enterica serovar enteritidis becomes Salmonella enteritidis).
The vast majority of Salmonella serotypes encountered in developed countries are
zoonotic pathogens. Reservoirs for these organisms include poultry, pigs, birds, cattle, cats, dogs,
rodents and turtles (AWWA, 2006). Infected humans and as a result, sewage, are also source of
Salmonella. Transmission of Salmonella occurs through the fecal-oral route, predominantly
through food. Drinking water is not often implicated as a source of Salmonella infection (Percival
et al., 2004). As Salmonella is a zoonotic pathogen, runoff from agricultural lands can provide a
mechanism for the transfer of animal fecal wastes to source waters.
The taxonomy of Shigella is much simpler than that of Salmonella. The genus is
categorized into four major serological groups. Shigella sonnei and Shigella flexneri are the two
species of importance as causes of gastrointestinal illness in developed countries (Percival et al.,
2004). Infected humans are the only significant reservoir (AWWA, 2006). Transmission is fecaloral, through drinking water or food that has been contaminated with human fecal wastes.
Person-person is also a significant route of exposure for Shigella, particularly among children.
Shigella is a human-specific pathogen and is not expected to be found in the environment
(AWWA, 2006). Thus contamination of water supplies is suggestive of a source of human fecal
contamination such as from sewage or on-site wastewater disposal systems.
Numerous outbreaks linked to contaminated drinking water have been reported
worldwide (Boring et al., 1971; White and Pedersen, 1976; Auger et al., 1981; CDC, 1996;
Angulo et al., 1997; Alamanos et al., 2000; Taylor et al., 2000; Chen et al., 2001). Schuster et al.
(2005) reported that Shigella and Salmonella were identified as the causative agent in 9 and 16
confirmed proposed or suspected drinking water outbreaks in Canada respectively over the years
1974-2001. In the United States, Salmonella and Shigella accounted for approximately 2% and
5% of drinking water outbreak reported from1991-2002 according to U.S. Surveillance data
(Craun et al., 2006). Common causes of waterborne outbreaks by these organisms are poor source
water, inadequate treatment or post-treatment contamination (e.g., by cross-connections)
(AWWA, 2006).
Both organisms give rise to acute, self-limiting gastrointestinal illness with symptoms of
diarrhoea, vomiting and abdominal pain. Shigella-associated illness is more dysenteric in nature,
marked by a more watery diarrhoea containing blood and mucus (AWWA, 2006). Once infected
recovering individuals may continue to shed either of these organisms in their faeces for days up
to several weeks or months. Published reports regarding the median infective doses for these two
organisms have suggested they may be as low as 103-105 organisms for Salmonella serotypes and
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Guidance on waterborne bacterial pathogens
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102-103 organisms for Shigella flexneri and Shigella sonnei (Hunter et al., 1997; Kothary and
Babu, 2001). The factors that contribute to the virulence of these organisms are still under
investigation. Both possess mechanisms that enable the bacteria to invade, survive, replicate and
disrupt the function of the human intestinal lining (Percival et al., 2004). In addition, Shigella
sonnei and Shigella flexneri are known to produce an exotoxin that affects intestinal water
absorption and retention (Percival et al., 2004).
B.1.2.1 Treatment technology
Salmonella and Shigella survival characteristics in water and their susceptibility to
disinfection have been demonstrated to be similar to those of coliform bacteria, including E. coli
(McFeters et al., 1974; Mitchell and Starzyk, 1975; Chang et al., 1985; Koivunen and HeinonenTanski, 2005). It is generally recognized that well-operated disinfection will be sufficient in
controlling Salmonella and Shigella in treated drinking water (AWWA, 2006).
B.1.2.2 Assessment
The absence of E. coli during routine verification should be an adequate indication of the
sufficient removal and inactivation of Salmonella and Shigella.
B.1.3 Campylobacter and Yersinia
Campylobacters are pathogenic bacteria found primarily in the intestinal tract of domestic
and wild animals, especially birds. Poultry, cattle, sheep and pigs are considered significant
reservoirs for these organisms (Percival et al., 2004; AWWA, 2006). Yersinia can be found in the
faeces of wild animals as well as domestic livestock such as cattle, pigs and sheep (Percival,
2004). It is the Campylobacter species C. jejuni, C. coli and C. upsaliensis, and the Yersinia
species Y. enterocolitica that are most important to the water industry (AWWA, 2006). Human
sewage also contains large number of both of these organisms.
Both Campylobacter and Yersinia enterocolitica are transmitted through the fecal-oral
route, mostly through contaminated food, and sometimes through water (Percival et al., 2004).
Person to person transmission of Campylobacter or Yersinia enterocolitica is uncommon
(Percival et al., 2004; AWWA, 2006).
Waterborne outbreaks of gastroenteritis involving Campylobacter jejuni and Yersinia
enterocolitica have been recorded on numerous occasions, with improper treatment, posttreatment contamination or consumption of untreated water supplies being the most frequent
causes (Eden et al., 1977; McNeil et al., 1981; Mentzing, 1981; Vogt et al., 1982; Taylor et al.,
1983; Lafrance et al., 1986; Sacks et al., 1986; Thompson and Gravel, 1986). In a review of
Canadian data on waterborne outbreaks for the period spanning from 1974-2001, Schuster et al.
(2005), reported that Campylobacter was implicated in 24 outbreaks and was second only to
Giardia (51 outbreaks) in outbreaks where a causative agent was identified. The most notable
Canadian waterborne outbreak was the May 2000 Walkerton outbreak involving Campylobacter,
and E. coli O157:H7 where faecally contaminated well water was not properly treated before
consumption (Clark et al., 2003). No outbreaks of Yersinia gastroenteritis have been reported for
municipal drinking water supplies in North America over the past two decades (Schuster et al.,
2005; Craun et al., 2006)
Campylobacter enteritis typically presents as flu-like symptoms and/or abdominal pain,
followed by a profuse watery diarrhoea caused by the presence of an enterotoxin similar to
cholera toxin (AWWA, 2006). A known, but rare complication of Campylobacter illness is
Guillian-Barré syndrome — a nervous system disorder causing rapidly progressing weakness of
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the muscles and nerves (Percival, 2004; AWWA, 2006). Yersinia enterocolitica-associated
gastroenteritis is associated with symptoms of fever, diarrhoea, abdominal cramps and
occasionally vomiting (AWWA, 2006). The gastrointestinal illnesses caused by both organisms
are considered to be self-limiting (Percival et al., 2004).
B.1.3.1 Treatment technology
Studies have demonstrated the susceptibility of Campylobacter species and Yersinia
enterocolitica to disinfectants commonly used in water treatment (Wang et al., 1982; Blaser et
al., 1986; Sobsey, 1989; Lund, 1996; Rose et al., 2007). It is generally recognized that treatment
technologies effective in the removal and inactivation of E. coli will be effective against these
pathogenic bacteria (AWWA, 2006).
B.1.3.2 Assessment
Studies have a lack of a correlation between indicator organisms (e.g., E. coli, total
coliforms) and the presence of Campylobacter and Yersinia in raw surface water supplies (Carter
et al., 1987; Lund, 1996; Hörman et al., 2004). Thus, E. coli may not be an adequate indicator of
the presence of both C. jejuni and Y. enterocolitica in source waters at all times. However, as it is
expected that properly operated treatment and disinfection technologies are effective in
controlling these organisms in treated drinking water, it is expected that the E. coli guideline is
sufficiently protective against their potential presence.
B.2
Other bacterial pathogens
B.2.1 Legionella
Legionellae are recognized human pathogens; they are a cause of respiratory illness which
can be serious for persons with weakened immune systems. They are free-living aquatic bacteria
that occur widely in water environments. The presence of Legionella is more of a concern for
water systems outside of municipal water treatment systems, such as cooling towers, hospital and
residential plumbing systems. However, the organisms are also capable of colonizing drinking
water distribution system biofilms. Legionella species exhibit a number of survival properties
that make them quite resistant to the effects of chlorination and elevated water temperatures.
The bacteria themselves are weakly Gram-negative, small, motile, rods that have precise
nutritional requirements and as a result do not grow well on culture media. At least 50 different
Legionella species have been identified, and approximately half of these species have been
associated with disease. L. pneumophila (serogroup 1) is the agent responsible for most cases of
illness in humans. Other than L. pneumophila, species causing far fewer infections but still
considered to be clinically relevant include: L. micdadei, L. bozemanii, L. longbeachae, and L.
dumoffi (Rheingold et al., 1984; Doyle and Heuzenroeder, 2002; Roig et al., 2003).
B.2.1.1 Sources and exposure
Legionella species are naturally present in a wide range of freshwater environments,
including surface water (Fliermans et al., 1981; Palmer et al., 1993) and groundwater (Brooks et
al., 2004; Costa et al., 2005). The bacteria are not considered to be enteric pathogens and are not
transmitted via the fecal-oral route. However, Legionella can occasionally be detected in human
fecal samples, as diarrhoea is a symptom of illness in a percentage of cases (Rowbotham, 1998).
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Similarly, animals are not reservoirs for Legionella (U.S. EPA, 1999).
Legionella can be isolated from human-made systems (e.g., cooling towers, hot water
tanks, shower heads, aerators). The presence of Legionella in these systems is almost exclusively
associated with biofilms (Lau and Ashbolt, 2009). In general, the amount of legionellae in source
waters is low compared with the concentrations that can be reached in human-made systems
(Mathys et al., 2008). In an investigation of biofilm formation and Legionella colonization on
various plumbing materials (Rogers et al., 1994), the numbers of biofilm-bound Legionella
spanned from 1 to 80 times those detected in free water. Biofilms are important for the survival
of the fastidious legionellae: they provide protection to Legionella, which are also able to utilize
nutrients supplied by other organisms in this nutrient-rich environment (Borella et al., 2005;
Temmerman et al., 2006; Lau and Ashbolt, 2009).
Some naturally occurring waterborne protozoa, such as Acanthamoeba, Hartmanella,
Naegleria, Valkampfia and Echinamoeba, can also harbour Legionella organisms (Rowbotham,
1986;Kilvington and Price, 1990; Kramer and Ford, 1994; Fields, 1996). Legionella can infect
and remain within the protozoan cyst form, where they are protected from disinfectants
(Kilvington and Price, 1990; Thomas et al., 2004; Declerk et al., 2007). They are also able to
multiply within these protozoa, which has been proposed as likely to be the only way that
Legionella replicate within aquatic systems (Abu-Kwaik et al., 1998; Thomas et al., 2004). Thus,
as well as offering protection, this association suggests a mechanism for the increase and
transport of L. pneumophila in human-made systems (Declerk et al., 2009).
Temperature is an additional factor that influences Legionella colonization of water
systems. Temperatures between 20°C and 50°C are hospitable for colonization, although
legionellae typically only grow to high concentrations at temperatures below 42°C (Percival et
al., 2004).
Plumbing systems outside of public water supply systems (e.g., in residential buildings,
hotels, institutional settings) are most commonly implicated in L. pneumophila infections (Yoder
et al., 2008). Since Legionella is a respiratory pathogen, systems that generate aerosols, such as
cooling towers, whirlpool baths and shower heads, are the more commonly implicated sources of
infection. The hot water supply system is commonly pinpointed as the origin of the
contamination (Hershey et al., 1997; McEvoy et al., 2000; Borella et al., 2004; Oliver et al.,
2005; Burnsed et al., 2007; Yoder et al., 2008). However, the cold water supply, when held
within the range of Legionella multiplication (25°C), has also been implicated (Hoebe et al.,
1998; Cowgill et al., 2005). Legionella infection can occur when people breathe in contaminated
aerosols. The bacteria have not been found to be transmitted from person to person (U.S. EPA,
1999).
Legionella contamination is particularly troublesome in hospitals, where susceptible
human populations are present and can be exposed to aerosols containing hazardous
concentrations of L. pneumophila. Within the community, large buildings such as hotels,
community centres, industrial buildings, and apartment buildings are most often implicated as
sources of outbreaks (Riemer et al., 2010). Studies have shown that contamination of domestic
hot water systems with Legionella can occur in single-family homes (Joly et al., 1985; Alary and
Joly, 1991; Stout et al., 1991; Marrie et al., 1994; Dufresne et al., 2011). In a study of hot water
plumbing systems in homes in the Quebec City area, Alary and Joly (1991) reported that
Legionella was detected in 39% (69/178) of hot water tanks with electric heaters, and in 0%
(0/33) of tanks with oil or gas-fired heaters. The authors further observed that in a proportion of
those homes whose hot water tanks tested positive for Legionella, the organism could also be
detected at distal locations such as faucets (12%) and showerheads (15%). The position of the
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heat source in the design of electrically-heated hot water tanks observed at the time of study was
cited as the reason for the difference in contamination between the two water heater types (Alary
and Joly, 1991). In the electric tanks, the heating elements were located above the bottom of the
heater, which could allow bottom sediments to remain at lower temperatures (< 50-60°C)
permissible for Legionella growth.
Similarly, evidence has been provided that sporadic cases of Legionnaires’ disease can
plausibly be acquired from aerosols in residential plumbing systems (Stout et al., 1992; Straus et
al., 1996; Lück et al., 2008). In a study conducted in the province of Quebec, Dufresne et al.
(2011) observed that among 36 legionellosis-confirmed patients residing in homes with domestic
hot water tanks, residential and clinical isolates of Legionella were microbiologically-related by
pulse-field gel electrophoresis in 14% (5/36) of the cases. Similar studies conducted in Pittsburgh
(Stout et al., 1992), and the state of Ohio (Straus et al., 1996) showed comparable results.
Persons thought to be at the highest risk of contracting Legionnaires’ disease are those
with lung conditions or compromised immune systems (e.g., persons receiving transplants or
chemotherapy, persons with diabetes or kidney disease). The risk of infection is higher among
persons 40-70 years of age, and the disease is seen more frequently in males than in females
(Percival et al., 2004). Other risk factors include smoking and excessive use of alcohol.
Legionnaires’ disease is considered a very rare cause of pneumonia in children. In contrast, age,
gender and smoking do not seem to be risk factors for Pontiac fever (Diederen, 2008).
The concentration of Legionella required to cause infection is not well understood
(Armstrong and Haas, 2008). It has been suggested that amoebae harbouring Legionella may
increase the potential for infectivity by providing a mechanism to expose humans to hundreds of
Legionella cells if inhaled or aspirated in an aerosol (Rowbotham, 1986; Greub and Raoult,
2004).
B.2.1.2 Health effects
There are two distinct illnesses caused by Legionella: Legionnaires’ disease and Pontiac
fever. Collectively, these illnesses are referred to as legionellosis. Legionnaires’ disease is a
serious respiratory illness involving pneumonia. Other features include: fever, cough and
headache; chest and muscle pain; and a general feeling of unwellness (malaise) (Fields et al.,
2002; CDC, 2008b). The time from the point of infection to the onset of symptoms is about 2–10
days, and the disease period can last up to several months. One problem in diagnosing
Legionnaires’ disease is a lack of any specific symptom that distinguishes it from other bacterial
pneumonias. Reported rates of Legionnaires’ disease in Canada over the period 2000-2004 (the
latest year for which data has been published) ranged from 0.13 to 0.20 cases per 100,000
population (PHAC, 2011). The mortality rate of Legionnaires’ disease in the United States as of
1998 was reported at roughly 10% and 14% for community-acquired and hospital-acquired cases,
respectively (Benin et al., 2002). Once in the lungs, Legionella is able to cause disease and avoid
human immune defenses by infecting macrophages – immune system cells which ordinarily
capture foreign bodies and present them to other cells for digestion (Fields et al., 2002).
Legionella replicates within these macrophages and then causes their death, which results in the
release of new organisms to continue the infection. Early diagnosis and antibiotic therapy are
keys to successfully treating Legionnaires’ disease.
Pontiac fever is a less serious respiratory illness that does not involve pneumonia and is
more flu-like in nature. The time to the onset of symptoms is 24–48 hours (AWWA, 2006; CDC,
2008a). Disease is self-limiting, and typically resolves without complications in 2–5 days (CDC,
2008b). No known fatalities have been reported with this illness. Pontiac fever is difficult to
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distinguish from other respiratory diseases because of a lack of specific clinical features. Experts
have speculated that disease may be caused by exposure to a mixture of live and dead Legionella
cells and non-Legionella endotoxin (Diederen, 2008). Antibiotic treatment is typically not
prescribed because of the short, self-limiting nature of the disease (CDC, 2008b).
B.2.1.3 Treatment technology
Successful control of Legionella in water supplies requires focused attention not only on
the organisms themselves, but also on the control of free-living amoebae and biofilms that
support their persistence.
Physical removal mechanisms used during drinking water treatment, such as coagulation,
flocculation, sedimentation, and filtration, will reduce the number of Legionella present in
finished water. Disinfectants shown to be effective in reducing the number of Legionella present
include: chlorine, monochloramine, chlorine dioxide, ozone and UV. In comparison with E. coli,
Legionella cells have been shown to be more resistant to chlorination (Delaedt et al., 2008; Wang
et al., 2010). Survival strategies exhibited by the organisms (colonization of biofilms and
residence within free-living amoebae) also further protect Legionella from the action of
disinfectants. In the distribution system, currently recommended disinfectant residuals are
sufficient to keep the concentration of non-biofilm-associated Legionella at levels that have not
been associated with disease (Storey et al., 2004; Delaedt et al., 2008). Hyperchlorination has
been employed as a control strategy; however, studies have demonstrated that Legionella residing
in biofilms or in cysts of Acanthamoeba polyphaga can survive following exposure to 50 mg/L
free chlorine (Kilvington and Price, 1990; Cooper and Hanlon, 2010). There is also the concern
of an increased potential for corrosion of plumbing systems with continued high concentrations
of chlorine (Kool et al., 1999).
Various alternative disinfection methods have been examined for their potential to control
Legionella colonization in the distribution system. Monochloramine has been shown to be more
effective than chlorine as a residual disinfectant against legionellae. Weintraub et al. (2008)
observed that converting from chlorine to monochloramine for residual disinfection in a
municipal distribution system resulted in a significant reduction in the number of distribution
samples, point-of-use sites and water heaters positive for Legionella colonization. Further, Kool
et al. (1999) reported that hospitals using monochloramine for secondary disinfection were less
likely to have reported outbreaks of Legionnaires’ disease than those using free chlorine.
Monochloramine is considered better able to penetrate into biofilms (LeChevallier, 1981), and is
more stable, therefore able to maintain its concentration over greater distances in the distribution
system (Kool et al., 1999).
Chlorine dioxide has demonstrated similar advantages over chlorine as a residual
disinfectant for Legionella control. Sidari et al. (2004) observed significantly decreased
Legionella concentrations at hot and cold point of use sites of a hospital’s plumbing system upon
switching to chlorine dioxide as the residual disinfectant. However, Health Canada (2008) has
determined that chlorine dioxide is not effective to maintain a disinfectant residual in the
distribution system.
It has been suggested that ozone may be a more effective disinfectant against Legionella
than chlorine, but its main drawback is that it does not stay in water sufficiently long to provide a
disinfectant residual (Kim et al., 2002; Blanc et al., 2005). Loret et al. (2005) observed that ozone
at a concentration of 0.5 mg/L was effective in reducing Legionella, protozoa and biofilms in a
model distribution system, but was not as effective as chorine (2 mg/L) or chlorine dioxide
(0.5 mg/L), which both showed longer residual concentrations in the system. Ozone at a
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concentration of 0.1-0.3 µg/mL was shown to be as effective as 0.4 mg/L free chlorine in
inactivating Legionella suspensions, producing a 2-log reduction of the organism within five
minutes in laboratory experiments (Dominique et al. 1988).
Copper-silver ionization systems have also received much study and have shown
effectiveness in controlling Legionella in drinking water supplies (Stout et al., 1998; Kusnetsov
et al., 2001; Stout et al., 2003; Cachafeiro et al., 2007). Stout et al. (1998) observed that coppersilver ionization (mean hot water tank concentrations of 0.29 mg/L and 0.054 mg/L, respectively)
was more effective than a superheat-and-flush method in reducing the recovery of Legionella
from a hospital distribution system. In a survey of the experiences of hospital systems using
copper-silver ionization, Stout et al. (2003) reported that following installation of the disinfection
systems, the percentage of hospitals reporting cases of (1) Legionnaires’ disease, and (2) positive
Legionella samples at more than 30% of the sites measured, had both been reduced to 0% from
100% and 47%, respectively, before the systems had been installed.
Additional measures recommended for distribution systems include temperature control;
control of water system design and construction to prevent the accumulation of biofilms,
sediments or deposits; and nutrient control strategies (Bartram et al., 2007; Bentham et al., 2007).
In plumbing systems in hospitals and large buildings, thermal disinfection (elevating hot
water to temperatures above 70°C, and flushing use points such as taps and showerheads) has
been routinely employed either on its own or in conjunction with chemical disinfection. Typically
this is recognized as a temporary control strategy as recolonization can occur within a few
months of treatment (Storey et al., 2004).
General recommendations regarding the control of Legionella in domestic plumbing
systems involve maintaining proper water temperatures. The National Plumbing Code of Canada
includes requirements of a minimum of 60°C for water temperature in hot water storage tanks, to
address the growth of Legionella (NRCC, 2010). Where increased hot water temperatures create
an increased risk of scalding for vulnerable groups (e.g., children, the elderly), appropriate safety
measures should be applied to limit the temperature to 49°C. Thermostatic or pressure-balanced
mixing valves can be installed to control the water temperature at the tap to reduce the risk of
scalding (Bartram et al., 2007; Bentham et al., 2007).
Control of Legionella in water systems outside of plumbing systems also requires
controlling its growth in biofilms. The heating, ventilation and air conditioning industry has
guidelines for reducing Legionella growth in cooling systems (ASHRAE, 2000) Hotel and
lodging industry requirements for the operation and maintenance of plumbing facilities, including
procedures for the proper disinfection of plumbing equipment in their facilities, are generally
specified under various public health regulations and/or legislation. Consulting with the
appropriate Provincial or Territorial Ministry of Health is advisable for obtaining information on
these requirements.
B.2.1.4 Assessment
The increasing importance of Legionella as a cause of human infection can be in part
linked to continued human development and the resulting dependence on human made plumbing
systems (Fields et al., 2002). Despite being ubiquitous in source waters, Legionella pneumophila
and other Legionella species have only been recovered in low concentrations from Canadian
drinking water supplies (Dutka et al., 1984; Tobin et al., 1986), and no illnesses have been linked
to these low concentrations. For these reasons, the presence of the organism is not sufficient
evidence to warrant remedial action in the absence of disease cases (Dufour and Jakubowski,
1982; Tobin et al., 1986).
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Due to the existence of Legionella outside of fecal sources in nature, E. coli is not
expected to be a reliable indicator of the presence of these bacteria. No suitable indicators have
been identified to signal increasing concentrations of Legionella in a building’s plumbing system.
There is some evidence that increasing Legionella concentrations are accompanied, or preceded,
by elevated HPC measurements (WHO, 2002). However, the correlation between HPC and
Legionella is not consistent.
Legionella have also been included on the U.S. EPA’s Candidate Contaminant List (CCL)
as one of the priority contaminants for regulatory decision making and information collection
(U.S. EPA, 2009). Guidelines or regulations that have been developed for Legionella in Canada,
the United States and other countries worldwide relate to control of the organism in water
environments outside of municipal water distribution networks (e.g., piped water systems,
cooling towers, health care facilities) (Cunliffe, 2007).
B.2.2 Mycobacterium avium complex
The Mycobacterium avium complex (Mac) is a grouping of environmental mycobacteria
that can cause illness in humans. The group consists of Mycobacterium avium (includes
subspecies: avium, sylvaticum and paratuberculosis); and Mycobacterium intracellulare
(Cangelosi et al., 2004). Mac organisms are considered ubiquitous in natural waters.
Transmission is primarily through contact with contaminated waters via either ingestion or
through inhalation (AWWA, 2006). Mac disease comes mainly in the form of lung infections,
and occurs largely in persons who have suppressed immune systems (Percival et al., 2004).
Mycobacteria themselves are motile rod to coccoid-shaped bacteria that have
characteristically high levels of waxy lipids in their cell wall. They are Gram negative, but are
more commonly considered to be “acid-fast” due to the way their cell walls respond to diagnostic
staining procedures (AWWA, 2006). Mac organisms are also referred to as “non-tuberculous” or
“atypical” mycobacteria. This is to distinguish them from the more well-known mycobacteria
species that are responsible for tuberculosis and leprosy that are not a concern for drinking water
(Nichols et al., 2004). Other environmental mycobacteria are known that have been linked to skin
infections through waterborne contact; but these are also of lesser importance to drinking water
supplies (Nichols et al., 2004).
B.2.2.1 Sources and exposure
Mac organisms are natural inhabitants of water and soil environments (Falkinham, 2004).
Water is considered the main reservoir (Percival et al., 2004; Vaerewijck et al., 2005), and the
organisms can be encountered in natural aquatic systems worldwide including marine waters and
fresh water lakes, streams, ponds and springs (Falkinham, 2004; Percival et al., 2004). Mac
organisms can be encountered in drinking water supplies, but generally in low numbers and at
low frequency (Peters et al., 1995; Covert et al., 1999; Falkinham et al., 2001; Hillborn et al.,
2006). However, Mac bacteria can survive in distribution system biofilms, and grow there to
reach significant populations (Falkinham et al., 2001). Following an 18-month survey of
Mycobacteria in drinking water of 8 water treatment plants, Falkinham et al. (2001) noted that
mycobacteria numbers were on average, 25,000-fold higher in distribution samples than samples
taken upstream in the treatment plant. Counts of M. intracellulare in biofilms were observed to
reach 600 CFU/cm2, on average (Falkinham et al., 2001). Feazel et al. (2009) observed that
Mycobacteria were enriched in plumbing system (showerhead) biofilms, reaching counts
100 times above those in water samples. In another study, Tsintzou et al. (2000) observed a
statistically significant decrease in the presence of environmental mycobacteria in drinking water
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samples after the replacement of the city’s water distribution network. The authors attributed the
reduction to the absence of distribution system biofilms (Tsintzou et al., 2000). Surveys of water
samples from water treatment plants and residential dwellings have reported Mac isolation rates
of 2-60% (von Reyn et al., 1993; Glover et al., 1994; Peters et al., 1995; Covert et al., 1999;
Hillborn et al., 2006). Hillborn et al. (2006) recovered M. avium from roughly 50-60% of pointof-use (POU) samples (cold-water taps) served by two water treatment plants. Concentrations
ranged from 200 to greater than 300 CFU/500 mL (Hillborn et al., 2006). Von Reyn et al. (1993)
isolated Mac organisms from 17-25% of water supply samples, collected from hot water taps at
patient care facilities (hospitals and clinics).
Other studies have reported a failure to isolate Mac organisms from water systems,
instead detecting only other non-Mac mycobacteria (von Reyn et al., 1993; Le Dantec et al.,
2002a; September et al., 2004; Sebakova et al., 2008). It has been suggested that the likelihood of
exposure to Mac bacteria in water is diverse in various areas of the world but in general, may be
less in developing countries (von Reyn et al., 1993, September et al., 2004). Mac organisms and
biofilms have also been found in other human-made systems such as: cooling towers (Pagnier et
al., 2009); ice-machines (LaBombardi et al., 2002); nebulizer reservoirs and toilets and sinks
(AWWA, 2006); and water meters (Falkinham et al., 2001). Studies have reported the isolation of
non-tuberculous mycobacteria from ground water, though M. avium has not been frequently
detected (Falkinham et al., 2001; Vaerewijck et al., 2005)
Similar to Legionella, the growth and survival of Mac organisms can be enhanced by their
ability to invade and survive in free-living amoebae such as Acanthamoeba polyphaga or A.
castellanii (Cirillo et al., 1997; Steinert et al., 1998). A key difference between Mac and
Legionella however, is that Mac organisms are able to replicate outside of amoebae, in biofilms
(Steinert et al., 1998; Vaerewijck et al., 2005).
The ubiquitous nature of Mac organisms results from their ability to survive and grow
under varied conditions. Mycobacteria can survive in water with little nutrients. Archuleta et al.
(2002) observed that M. intracellulare was capable of surviving for over a year in reverse
osmosis deionized water. Mac organisms have also been shown to grow in natural waters over
wide ranges of pH (5-7.5), salinity (0-2%) and temperature (10-51°C) (Sniadack et al., 1992;
Falkinham et al., 2001). Water conditions that have been identified as being more favourable for
the growth of Mac organisms include high levels of humic and fulvic acids, high zinc
concentrations, low pH and low dissolved oxygen levels (Kirschner et al., 1992; Kirschner et al.,
1999; Vaerewijck et al., 2005)
Infection through contact with M. avium and M. intracellulare has been well documented
(Wendt et al., 1980; Grange, 1991; Glover et al., 1994; Montecalvo et al., 1994; von Reyn et al.,
1994; Kahana et al., 1997; Aronson et al., 1999; Mangione et al., 2001). Inhalation of
contaminated aerosols, during contact with contaminated hot tubs, spa pools or similar facilities
is most frequently cited as the route and source of infection (Kahana et al., 1997; Mangione et al.,
2001; Rickman et al., 2002; Cappulluti et al., 2003; Lumb et al., 2004; Sood et al., 2007). Personperson transmission of the organisms is thought to be uncommon (Nichols et al., 2004;
Falkinham, 1996). Evidence of the link between water supplies, particularly hot water supplies
and Mac infection has also been provided (von Reyn et al., 1994; Tobin-D’Angelo et al., 2004;
Marras et al., 2005). Von Reyn et al. (1994) reported the detection of the same strain of M. avium
in patients and hospital potable water supplies to which they had been exposed; but not in water
supplies collected from patient’s homes. Marras et al. (2005) documented a case of Macassociated hypersensitivity pneumonitis where the patient strain was recovered from the shower
and bathtub from the patient’s home, but not the hot tub. Despite these links, it has been
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suggested that hospital and domestic drinking water-related cases represent a small proportion of
Mac illness (von Reyn et al., 1994, Phillips et al., 2001). The infectious dose of Mac has not been
well established. Rusin et al. (1997) proposed an oral infectious dose for mice of 104 to 107
organisms. True estimations of the inhaled infectious dose would be dependent upon (among
other factors) the virulence of the organism and the immune status of the host.
B.2.2.2 Health effects
Mac organisms largely cause opportunistic infections in humans. The vast majority of
people exposed to Mac do not develop disease (Field et al., 2004). Infections occur mostly in
individuals who have weakened or suppressed immune systems (AIDS patients, the elderly, the
very young) or persons with underlying conditions such as cystic fibrosis. Mac disease rarely
occurs in healthy people (Field et al., 2004). Mac organisms have low pathogenicity, so
individuals can become colonized with the organisms without any adverse health effects.
The main symptom of Mac lung infection is a chronic productive cough (cough with
phlegm, saliva or mucus) (Field et al., 2004). Other symptoms can include fever, night sweats,
fatigue and weight loss (Percival et al., 2004). However it has been suggested that the secondary
symptoms are less common unless the individual has extensive lung disease (Crow et al., 1957;
Field et al., 2004). In HIV/AIDS sufferers, Mac infection can spread to other parts of the body,
including joints, skin, blood, liver and brain; and the disease can be debilitating and lifethreatening for these patients (Percival et al., 2004). A possible role for Mac organisms in the
development of Crohn’s disease, an inflammatory bowel disease, has been suggested, but
supporting data is presently inconclusive (Feller et al., 2007; Behr and Kapur, 2008).
Epidemiological studies have shown evidence of a strong association between Mycobacterium
avium paratuberculosis and the disease, but the causality of this association is unknown (Feller et
al., 2007; Abubakar et al., 2008). Mac can also be a cause of lymphadenitis in children (lymph
node infection - likely acquired through the oral route) and hypersensitivity pneumonitis in adults
(inflammation of lung alveoli due to inhaled organic dusts) (Tortoli, 2009).
The true prevalence of Mac infections is not known, as it is not a reportable illness in
Canada or the United States. Estimates of the rate of Mac-related pulmonary disease in the U.S.
have been put from 1-2 cases to as high as 5 cases per 100,000 persons per year based on
epidemiological studies conducted in various American cities (Reynolds et al., 2001; Marras and
Daley, 2002). Marras et al. (2007) estimated the prevalence of pulmonary non-tuberculous
mycobacteria in Ontario to range from 9-14 positive isolations per 100,000 population over the
years from 1997-2003. The authors further reported that overall, Mac were isolated in roughly
60% of the cases (Marras et al., 2007).
Mac diseases are treatable, but the clearing of these infections can be difficult, and
treatment can have a high rate of failure (Field et al., 2004). Mycobacteria have demonstrated
strong resistance to antimicrobial agents (Daley and Griffith, 2010). Antibiotics are delivered at
high doses and often require a long administration period (e.g., several months to over a year)
(Percival et al., 2004; Daley and Griffith, 2010).
B.2.2.3 Treatment technology
Water treatment technologies commonly used, including chemical disinfection and
physical removal methods, have been tested for their ability to inactivate or remove mycobacteria
from water supplies. Of these technologies, the most effective has been physical removal using
sand filtration and coagulation–sedimentation techniques. In one study, Falkinham et al. (2001)
observed that water treatment plants treating surface water sources reduced mycobacteria
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numbers by 2-4 log through filtration, and primary disinfection. A significant association
between the frequency of detection of M. avium and high raw water turbidity was also reported.
The authors were careful to note that reducing turbidity could represent one approach to reducing
mycobacteria in drinking water, but that this procedure alone may not be completely sufficient to
eliminate M. avium from the distribution system (Falkinham et al., 2001). Mac organisms are
more resistant to the commonly used disinfectants. The highly hydrophobic quality of the
organism’s cell wall is thought to be largely responsible for this increased resistance
(LeChevallier, 2004).
For chlorination, Le Dantec et al. (2002b) reported varying chlorine sensitivities among a
collection of various mycobacteria isolated from the distribution system (note: Mac organisms
were not isolated in this study). The authors calculated that a CT of 60 mg·min/L (e.g., 0.5 mg/L
for 2 hours) would result in a log reduction for environmental mycobacteria ranging from 1.5 to
4 logs. Taylor et al. (2000) provided data on the susceptibility of environmental and patient
isolates of M. avium to various disinfectants: chlorine, monochloramine ozone and chlorine
dioxide. The mean CT99.9 (mg·min/L) values for the individual disinfectants were: chlorine: (51204), monochloramine (91-1710), ozone (0.10-0.17) and chlorine dioxide: (2-11). The authors
did note that there was significant variation in the susceptibility of different strains (Taylor et al.,
2000).
In another study using chlorine dioxide, Vicuna-Reyes et al. (2008) reported CT99.9 values
ranging from 3-36 mg·min/L (5-30°C), prompting the authors to conclude that the disinfectant
can be effective in controlling mycobacteria. The CT values necessary for inactivation of Mac
have been reported to range from near equivalency to a few times greater (monochloramine); to
tens to hundreds of times greater (ozone, chlorine dioxide); to over two thousand times greater
(chlorine) than that necessary to inactivate E. coli (Taylor et al., 2000). Data have been provided
suggesting that mycobacteria are more sensitive than Cryptosporidium oocysts to chlorine,
monochloramine chlorine dioxide and ozone, and is equal or more sensitive than Giardia to all of
these with the exception of free chlorine (Jacangelo et al., 2002; LeChevallier, 2004).
In UV disinfection studies, Hayes et al. (2008) demonstrated that patient and
environmental strains of M. avium and M. intracellulare exhibited greater than 4-log reduction at
UV fluences less than 20 mJ/cm2. The authors concluded that Mac organisms in free-suspension
could be readily inactivated by UV doses commonly employed in drinking water treatment
(Hayes et al., 2008). LeChevallier et al. (2004) reported that UV values required to inactivate
mycobacteria are in the range of those required for other vegetative bacteria.
Even with good removal of organisms from the source water, the number of Mac
organisms may increase in the distribution system (Falkinham et al., 2001). Residing within
biofilms or free-living amoebae can further increase Mac organism resistance to inactivation.
Steed et al. (2006) observed that M. avium and M. intracellulare cells in biofilms were up to 1.84 times more resistant than cells in free suspension when exposed to chlorine. Miller and
Burmudez (2000) showed that M. avium growth within Acanthamoeba reduced the bacteria’s
susceptibility to antibiotics. As with Legionella, successful control of Mac organisms requires
attention on the control of free-living amoebae and biofilms that support their persistence.
Mac organisms have also demonstrated resistance to elevated temperatures. Several
authors have reported recovery of M. avium from hot water systems at temperatures between 50
and 57°C (DuMoulin et al., 1988; von Reyn et al., 1994; Covert et al., 1999; Norton et al., 2004).
Additional factors thought to have a role in encouraging growth in the distribution system include
high assimilable organic carbon levels, as well as distribution system materials and construction
(e.g., pipe materials, gaskets, coatings, corroded pipes, dead ends, spaces, long storage times)
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(Falkinham et al., 2001). Similarly to distribution system control strategies described for
Legionella (Bartram et al., 2007; Bentham et al., 2007), temperature control; control of water
system design and construction to prevent the accumulation of biofilms, sediments or deposits;
and nutrient control strategies should also prove effective in the control of Mac organisms.
B.2.2.4 Assessment
No suitable indicators have been identified to signal increasing concentrations of Mac
organisms in water systems. For example, studies have found no relationship between the
numbers of non-tuberculous mycobacteria recovered from reservoir water and coliform counts,
HPCs, and total and free chlorine levels (Glover et al., 1994; Aronson et al., 1999). There is some
evidence that M. avium presence is associated with turbidity in raw waters (Falkinham et al.,
2001), but further exploration of this issue is needed.
Currently, the presence of mycobacteria in water is not regulated by any country or
international organization, including Canada. The U.S. EPA has identified M. avium and M.
intracellulare as waterborne health-related microbes that need additional research on their health
effects, their occurrence in water, and their susceptibility to treatment methods (Reynolds, 2001).
These organisms have also been included in a list of candidate contaminants for possible
regulation by the U.S. EPA (2009). At the present time, there is not sufficient information to
warrant actions based on the presence of the organisms in the absence of disease.
B.2.3 Aeromonas
The genus Aeromonas has gained public health recognition as organisms that can cause
opportunistic infections in humans. Species of Aeromonas have been associated with
gastroenteritis, however understanding of the role the organisms play as a cause of diarrhoeal
illness is presently incomplete. Skin, wound and soft tissue infections with Aeromonas species as
a result of exposure to contaminated water in non-drinking water scenarios have been well
documented. It is believed that drinking water has the potential to serve as a route of
transmission, but direct evidence of Aeromonas as a cause of drinking water-acquired
gastrointestinal illness is lacking.
Aeromonads are Gram-negative, short rod-shaped bacteria that share some similarities
with Vibrio and E. coli. They are universally found, occurring naturally in virtually all water
types. The genus Aeromonas contains more than 17 distinct genetic species. Three species: A.
hydrophila, A. veronii biovar sobria (syn. A. sobria) and A. caviae, account for roughly 85% of
human infections, and are therefore considered to be the species of most importance for drinking
water systems (Janda and Abbott, 1998; 2010).
B.2.3.1 Sources and exposure
Aeromonas species can be found in virtually all surface water types (freshwater, marine,
and estuarine) in all but the most extreme conditions of pH, salinity and temperature (Percival et
al., 2004; AWWA, 2006). They are less frequently detected in groundwater, with their presence
in these systems typically indicating well contamination (Havelaar et al., 1990; Massa et al.,
2001; Borchardt et al., 2003).
Aeromonads are recognized animal pathogens (Percival et al., 2004; AWWA, 2006). The
organisms have been isolated from the gastrointestinal tract and infected tissues of a number of
cold-blooded and warm-blooded animals, most notably fish, birds, reptiles and domestic
livestock (U.S. EPA, 2006; Janda and Abbott, 2010). They also have been recovered from retail
food items such as meat, poultry and dairy products (Janda and Abbott, 2010). It has been
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suggested that animals may be an environmental reservoir for Aeromonas (Janda and Abbott,
2010).
The organisms are not considered to be natural fecal pathogens (U.S. EPA, 2006).
Aeromonas species are not normally found in human faeces in high numbers (Janda and Abbott,
2010); however a small percentage of the population can carry the bacteria in their intestinal tract
without showing symptoms of disease (von Gravenitz, 2007). Estimates of the prevalence of
Aeromonas in human fecal samples worldwide have been roughly put at 0-4% for asymptomatic
persons and as high as 11% from persons with diarrhoeal illness (Burke et al., 1983; U.S. EPA,
2006, von Gravenitz, 2007; Khafanchi et al., 2010). Individual studies have observed rates that
have been as high as 27.5% and 52.4% for asymptomatic persons and diarrhoeal illness cases
respectively (Pazzaglia et al., 1990; 1991). Numbers of Aeromonas are much higher in sewage,
with concentrations of >108 CFU/mL having been reported (Percival, 2004).
Levels of Aeromonas in clean rivers, lakes, and storage reservoirs, have generally been
reported to be in the range of 1-102 CFU/mL (Holmes et al., 1996). Surface waters receiving
sewage contamination and nutrient-rich waters in the warmer summer months may reach
concentrations of 103 - 105 CFU/mL (Holmes et al., 1996; U.S. EPA, 2006). Groundwaters
generally contain less, with less than 1 CFU/mL (Holmes et al., 1996). Drinking water
immediately leaving the treatment plant is typically in the range of <1 to 102 CFU/mL (Holmes et
al., 1996; U. S. EPA, 2006; Pablos et al., 2009; Janda and Abbott, 2010) , with potentially higher
concentrations in drinking water distribution systems, (Payment et al., 1988; Chauret et al., 2001;
U.S. EPA, 2006). Concentrations in individual environments can be expected to vary, however,
The organisms can survive over wide ranges of pH (5-10) and temperature (2-42°C)
(Percival, 2004). Water temperature is particularly important to Aeromonas growth. In temperate
climes during the warmer months of the year, the bacteria have been shown to be more readily
detected from source waters and water distribution systems (Chauret et al., 2001; U.S. EPA,
2006; Janda and Abbott, 2010). Aeromonads are also very versatile nutritionally. They are
capable of growing to elevated numbers in water with high organic content and can also survive
in low nutrient waters (Kersters et al., 1996).
Similar to other bacteria, Aeromonas species can enter into a viable-non-culturable (VNC)
state under stressful conditions in aquatic environments. There is some debate at to what effect
this state has on a species’ viability and pathogenicity. Maalej et al. (2004) reported that cells of a
strain of A. hydrophila rendered non-culturable under marine stress conditions lost haemolytic
and cytotoxic properties; but that these could be regained following recovery at warmer
temperatures. In contrast, Mary et al. (2002) observed that VNC cells of A. hydrophila lost
viability, and this could not be regained following a temperature upshift to 25°C. It has been
suggested that survival properties may differ depending on the species and strain of Aeromonas
(Brandi et al., 1999; Mary et al., 2002).
The organisms have been detected in the distribution systems of chlorinated drinking
water supplies worldwide (Chauret et al, 2001; Emekdas et al., 2006; Langmark et al., 2007;
September et al., 2007). As with other bacterial pathogens, the presence of biofilms and freeliving amoebae have been identified as factors contributing to higher concentrations of
Aeromonas encountered in drinking water distribution systems relative to finished water
(Rahman et al., 2008; September et al., 2007). During an assessment conducted as part of their
Unregulated Contaminant Monitoring Regulations, the U.S. EPA (2002) provided data indicating
that Aeromonas could be detected in 11% of municipal systems serving greater than 10,000
persons and 14% of systems serving less than 10,000 persons. The concentrations of Aeromonas
reported were less than 10 CFU/100 mL in 78% of the samples (U.S. EPA, 2002). Limited
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studies have been conducted on Aeromonas-protozoa interactions within the municipal supplies.
Rahman et al. (2008) observed that the bacteria may use the free-living amoebae Acanthamoeba
as a reservoir to improve transmission and for protection from disinfectants.
Exposure to Aeromonas species through direct contact of wounds or skin follicles with
contaminated waters has been reported for recreational-type water environments such as lakes,
rivers, swimming pools and hot tubs (Gold and Salit, 1993; Manresa, 2009). Unusual water
situations brought about by floods or disaster events can be expected to create similar
opportunities for Aeromonas exposure. Wound infection with species of Aeromonas was a
problem among victims of the Thailand tsunami as a result of exposure to contaminated
floodwaters (Hiransuthikul et al., 2005). Exposure to Aeromonas in contaminated floodwaters
was also expected amongst victims and rescue workers following Hurricane Katrina (Presley et
al., 2006). Person-person transmission of Aeromonas resulting in infection is not expected to
occur (U.S. EPA, 2006).
The evidence for acquiring Aeromonas infection through the ingestion of drinking water
is not well established, and the subject is one of debate (von Gravenitz et al., 2007). The presence
of Aeromonas in finished drinking water supplies and distribution samples has been well
documented suggesting a possible route of transmission (LeChevallier et al., 1980; Payment et
al., 1988; Borchardt et al., 2003; Emekdas et al., 2006; Kuhn et al., 2007; Scoaris et al., 2008).
However, other findings have been cited which oppose this suggestion. Epidemiological
investigations have demonstrated little evidence of direct connections between patient isolates of
A. hydrophila with isolates recovered from their drinking water supplies. Borchardt et al. (2003)
observed that Aeromonas isolates were infrequently found in stool samples of gastroenteritis
patients and that those detected were not genetically related to isolates recovered from drinking
water. Additionally, researchers have cited the virtual absence of reported waterborne outbreaks
of diarrhoea against the near universal presence of Aeromonas in water environments as evidence
supporting that transmission of these organisms occurs by a mechanism other than through
drinking water (von Gravenitz, 2007; Janda and Abbott, 2010). Some researchers have speculated
that for many fecal isolates of Aeromonas, colonization of the human gastrointestinal tract may
only be fleeting (Janda and Abbott, 2010).
The ingested dose of Aeromonas necessary to cause gastrointestinal infections is
uncertain. Limited study has suggested that a high dose is required (U.S. EPA, 2006; Janda and
Abbott, 2010). In an early volunteer feeding study, Morgan et al. (1985) reported that only 2 of
57 individuals developed diarrhoea following ingestion of A. hydrophila strains at doses of up to
1010 CFU. It has been speculated that the concentrations required to cause illness are much higher
than the numbers that would typically be found in treated drinking water supplies (U.S. EPA,
2006).
Recently, in a large survey of clinical and waterborne strains of Aeromonas collected
from across the United States and worldwide, Khafanchi et al. (2010) reported detecting 3
isolates belonging to the A. caviae group that were genetically indistinguishable and possessed
the same virulence factors. The authors suggested that these findings provided the first evidence
of human infection and colonization by a waterborne Aeromonas strain (Khafanchi et al., 2010).
B.2.3.2 Health effects
Aeromonas-associated diarrhoea has been encountered worldwide, mostly in normally
healthy persons across all age groups (Janda and Abbott, 2010). Having low stomach acidity,
receiving antimicrobial therapy or having compromised immune function (e.g., from HIV
infection or through underlying disease – especially liver disease) are thought to be associated
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risk factors (Merino et al., 1995; Percival, 2004, von Gravenitz, 2007; Janda and Abbott, 2010).
The distinction of Aeromonas as a cause of gastrointestinal illness is controversial (von
Gravenitz, 2007; Janda and Abbott, 2010). Case reports and a small number of foodborne
outbreaks have linked the presence of Aeromonas to cases of diarrhoeal disease (U.S. EPA, 2006;
Janda and Abbott, 2010). However at the present, no outbreaks of gastrointestinal illness have
been reported for which a strain of Aeromonas has been definitely identified as the causative
agent (Janda and Abbott, 2010). Furthermore, researchers have been unable to find an animal
model in which Aeromonas-mediated gastrointestinal illness can be replicated (U.S. EPA, 2006;
Janda and Abbott, 2010).
Where Aeromonas species have been associated with gastroenteritis, the most common
symptom is watery diarrhoea that has been accompanied by fever and abdominal pain (Janda and
Abbott, 2010). Far less commonly, Aeromonas has also been identified in association with other
forms of gastrointestinal illness ranging from a dysenteric type of illness with bloody stools, to a
chronic, or subacute watery diarrhoea (Janda and Abbott, 2010). Aeromonas infections can also
be asymptomatic, with individuals shedding the bacteria in their stools, but not showing any
symptoms of disease (Percival, 2004).
Aeromonas species have been positively isolated from skin, wound and soft-tissue
infections (Percival, 2004; Janda and Abbott, 2010). These can range in scope from mild
irritations (e.g., pus-filled lesions) to cellulitis (inflammation below the skin), to, in extreme
cases, necrotizing fasciitis (flesh-eating disease) (Janda and Abbott, 2010). These are often the
result of trauma or penetrating injury from occupational or recreational water exposure, and are
generally seen more frequently in adults than children. Aeromonas has also recently been
implicated in respiratory infections. However these have been rare and have largely been caused
by near drownings or aspirations of contaminated waters unrelated to drinking water supplies
(Janda and Abbott, 2010)
Factors responsible for the pathogenicity and virulence of Aeromonas species or strains
are poorly understood. A number of potential virulence components have been identified that
would appear to enable the organisms to behave as human pathogens. These include such things
as pili, fimbriae and flagella for attachment and colonization; external lipopolysaccharides,
capsules or surface layers to assist in evading host defenses; and toxins, hemolysins, proteases
and other enzymes for causing damage to host cells (von Gravenitz, 2007; Janda and Abbott,
2010). Current studies have been unable to specifically pinpoint which combination of factors
would make a strain of Aeromonas behave as an enteropathogen (Janda and Abbott, 2010).
Research has identified that a known diarrhoea-causing strain of A. hydrophila possesses four
prospective virulence factors: two hemolysins (named Act and HlyA), a heat-stable enterotoxin
(Ast) and a heat-labile enterotoxin (Alt) (Erova et al., 2007; Janda and Abbott, 2010). Despite
such findings, the role and relative significance of each remains uncertain, as studies have also
found these factors distributed among numerous clinical and environmental strains in different
combinations (Erova et al., 2007; von Gravenitz, 2007; Castilho et al., 2009; Janda and Abbott,
2010). It has been proposed that only certain subsets of Aeromonas strains have the ability to
cause disease (Janda and Abbott, 2010).
Aeromonas is not a reportable organism in North America, or in most countries
worldwide (PHAC, 2011; CDC, 2011; Janda and Abbott, 2010). Of the case reports or outbreaks
of Aeromonas-related illness encountered in the literature, most have been tied to food, hospitals,
travel, non-water environments or are unknown. At present, no epidemiological evidence has
been provided linking an Aeromonas outbreak to ingestion, inhalation or skin contact with treated
drinking water supplies (U.S. EPA, 2006; von Gravenitz, 2007; Janda et al., 2010).
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As Aeromonas-related gastrointestinal illness is mild and self-limiting, treatment for
infection is generally not necessary. However, for other presentations of infection, antibiotic
therapy is usually implemented. Aeromonads are resistant to ampicillin and a variety of other βlactam antibiotics including penicillin and some cephalosporins (Percival, 2004; Janda and
Abbott, 2010).
B.2.3.3 Treatment technology
As mentioned previously, aeromonads are ubiquitous in many water environments.
Consequently, they will be present in most source waters used for drinking water production.
Nonetheless, existing evidence indicates that current treatment and disinfection methods can
effectively remove Aeromonas from treated drinking water. Data from pilot-scale (Harrington et
al., 2003; Xagoraraki et al., 2004) and full-scale (Chauret et al., 2001; El-Taweel and Shaban,
2001; Yu et al., 2008) investigations have demonstrated that well-operated conventional filtration
systems (coagulation-flocculation-sedimentation-rapid rate gravity sand filtration) are capable of
Aeromonas removals of up to 4-log. In a pilot-scale conventional treatment study, Xagoraraki et
al. (2004) observed that reducing filter effluent turbidity to less than 0.2 NTU resulted in A.
hydrophila removals of greater than 3-log to just under 4-log (median: 3.5 log). Yu et al. (2008)
investigated the effectiveness of different water treatment processes in removing Aeromonas as
measured using both culture-based and real-time PCR detection methods. Conventional filtration
(3 full-scale plants) reported removals of culturable Aeromonas ranging from > 0.3 log to 4 log
(Yu et. al., 2008). The authors further reported that no culturable Aeromonas could be detected
after sedimentation (Yu et al., 2008). Log removals as measured by real-time PCR detection
correlated well with, but were routinely lower than, those demonstrated by the culture-based
detection method (Yu et al. 2008).
For slow sand filtration, the authors examined 2 full-scale and 1 pilot-scale plants,
reporting log removals of greater than1 log, greater than 1.8 log for the full-scale plants and
greater than 1 log for the pilot-scale plant. Culturable Aeromonas was not detected in samples
collected post-filtration (Yu et al., 2008). Meheus and Peters (1989) reported similar results for
slow sand filtration, observing Aeromonas removals of 98-100%.
With membrane filtration, the full-scale plants included in the Yu et al. (2008) study
demonstrated a capability of removing culturable Aeromonas by greater than 3.8 and 4 logs.
Aeromonads are susceptible to inactivation by disinfectants commonly used in the
drinking water treatment, such as chlorine, monochloramine, chlorine dioxide, ozone and UV
(Knoechel et al., 1991; Medema et al., 1991, Sisti et al., 1998; U.S. EPA, 2002; 2006). For
chlorination, Sisti et al. (1998) reported Aeromonas T95 values (5°C, inoculum ~104 cells) of 5
min at 0.6 mg/L, and of 68 min at 0.05 mg/L free chlorine in a lab-scale chlorination experiment.
The authors also found Aeromonas (clinical strains) to be more susceptible to chlorine than E.
coli (clinical strains). Free chlorine concentrations of 0.14 mg/L (10°C) and greater than
0.5 mg/L (20-37°C) were sufficient to produce a 5-log inactivation of clinical and nosocomial
strains of Aeromonas within 5 min in an experiment conducted by Chamorey et al. (1999). In
contrast, de Oliveira Scoraris et al. (2008) observed that the majority of Aeromonas strains (water
and culture collection strains) were not killed after 1 minute exposure to free chlorine at
1.2 mg/L.
Chauret et al. (2001) conducted a study at both full-scale and pilot-scale simultaneously to
assess the presence of Aeromonas in source water and at various sites within the treatment plant
and distribution system and to assess biofilm formation. The authors noted no detectable
Aeromonas in treated water immediately after secondary disinfection with chloramine
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(concentration range: 2-3 mg/L), despite observing counts ranging from <1 to 490 CFU/100 mL
after chlorine disinfection (pre-filtration) and post-GAC filtration.
With chlorine dioxide, Medema et al. (1991) reported CT99 values of 0.04-0.14 mg·min/L
for a drinking water strain of A. hydrophila. In the same study, a naturally occurring Aeromonas
population (predominantly A. sobria) was observed to be slightly more sensitive with a reported
CT99 of 0.1 mg·min/L.
For UV disinfection, data produced by the U.S. EPA suggested the capability for a 1 and
2 log inactivation of A. hydrophila at doses of 3 and 8 mWs/cm2 respectively (equivalent to 3 and
8 mJ/cm2) - doses significantly less than those commonly employed in water treatment (U.S.
EPA, 2002).
In the distribution system, maintaining an adequate disinfectant residual should provide
control of Aeromonas in the finished water. The potential exists for Aeromonas to regrow in the
distribution system, however. During a year-long survey of a major drinking water distribution
system in Scotland, Gavriel et al. (1998) reported that although Aeromonas was not detected in
water samples collected downstream from chlorination prior to the distribution network; it could
be occasionally recovered from distribution samples, even at locations maintaining substantial
residual chlorine doses (> 0.2 mg/L). Similarly, other studies have demonstrated that Aeromonas
could be detected in municipal distribution systems at locations having temperatures below 14°C
and chlorine residuals greater than 0.2 mg/L (Chauret et. al, 2001; Pablos et al., 2009)
Elimination of Aeromonas in the distribution system once the organisms become
established in biofilms can be difficult (Holmes and Nicholls, 1995; Gavriel et al., 1998;
Langmark et al., 2007). Elements important for helping to control Aeromonas growth include
limiting the number of organisms entering the distribution system through effective treatment and
maintenance, maintaining low water temperatures, providing appropriate free chlorine residuals,
and limiting the levels of organic carbon compounds (WHO, 2010).
B.2.3.4 Assessment
Some studies have been undertaken to determine if the indicators currently used in the
drinking water industry, including E. coli, total coliforms, and HPC, can be used as surrogates for
the presence of Aeromonas. Several studies have showed no evidence of a relationship between
Aeromonas incidence and coliforms, E. coli, or HPCs (Holmes et al., 1996; Gavriel et al., 1998;
Fernandez et al., 2000; Pablos et al., 2009). Although no direct correlation exists between
Aeromonas populations and total HPC counts, the organisms do make up a portion of HPC
bacteria found in water, and are detected by HPC tests (Pablos et al., 2009). The Netherlands
have established drinking water standards for A. hydrophila, consisting of a median value (1 yr
period) of 20 CFU/100 mL in water leaving the treatment plant and a 90th percentile value (1 yr
period) of 200 CFU/100 mL in distribution system water (van der Kooij, 2003; Pablos et al.,
2009). These values have been based on an assessment of achievability and motivated by a
precautionary approach, rather than on the public health significance of their occurrence in
drinking-water (WHO, 2002).
Aeromonas is not considered an indicator of fecal contamination or treatment failure (U.S.
EPA, 2002). The organisms have been proposed as a possible supplemental indicator of drinking
water quality by relating to the presence of biofilm. Therefore, if there are significant increases in
Aeromonas concentrations in a drinking water supply, this indicates a general deterioration of
bacteriological quality.
When looking at the overall public health significance of A. hydrophila in drinking water,
further epidemiological studies are needed for a better understanding of the relationship between
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Aeromonas illness and the presence of these organisms in drinking water. Based on the current
evidence, treated drinking water likely represents a very low risk. It has been proposed that in
comparison to other possible pathogens that can potentially be acquired through drinking water,
Aeromonas is at the low end of the scale in terms of relative risk (Rusin et al., 1997; Janda and
Abbott, 2010). Nevertheless, it is advisable to minimize Aeromonas in drinking water supplies as
much as is practical until its public health significance has been fully investigated.
B.2.4 Helicobacter pylori
Helicobacter pylori is a recognized human pathogen that can colonize the human
stomach. The understanding of how this organism is spread is still quite limited, however it is
believed that there are a few routes of transmission, including through drinking water (Percival
and Thomas, 2009). Disease is benign for the most part in the majority of persons infected, but
more serious disorders such as peptic ulcers or stomach cancer can develop in a small percentage
of cases.
Helicobacters are Gram-negative, motile small curved rods that are closely related to
Campylobacter. The organisms have two distinct forms, a spiral rod shape and a shorter coccoid
form, which is taken on under conditions of stress. To date, the coccoid form has been found to
be non-culturable. The genus Helicobacter has at least 25 species as determined by DNA
sequencing – of which H. pylori is the species of relevance for the water industry. Other
Helicobacter species have been detected in humans that have been associated with gastric illness;
however these are not considered to be as prevalent.
B.2.4.1 Sources and exposure
The primary reservoir identified for H. pylori is the human stomach (Dunn et al., 1997;
Brown, 2000). There has been evidence that some animals can be infected by H. pylori (cats,
dogs, sheep, primate monkeys) but presently the consensus is that they do not hold a significant
role as reservoirs in transmitting this organism to humans (Baele et al., 2009; Haesebrouck et al.,
2009). Although H. pylori has been cultured from human faeces, at present isolation from water
using culture methods has not been successful (Percival and Thomas, 2009). It is believed that
the spiral culturable form rapidly transforms into a viable, non-culturable state (coccoid form) in
the water environment. This is thought to be a stress response to environmental changes which
can include: temperature, low nutrient availability and differences in osmolarity (Adams et al.,
2003; Percival and Thomas, 2004).
Exact details on the transmission of H. pylori remain unclear (Bellack et al., 2006). Based
on epidemiological findings, a higher risk of H. pylori infection exists among persons of low
economic status living in crowded conditions or unhygienic environments (Brown, 2000; Gomes
and Demartinis, 2004). Transfer mechanisms that have been proposed include gastric-oral, oraloral and fecal oral (Percival and Thomas, 2009). Overall, it is speculated that person-person
transfer is the most likely route of transmission (Brown, 2000). The fact that it has not yet been
possible to culture viable Helicobacters from the water environment has raised questions
regarding the possibility of waterborne transmission. Nevertheless, there has been significant
evidence provided in support of water as an important source of infection. Molecular techniques
(PCR, Fluorescent in-situ DNA hybridization [FISH]) have been used to confirm the presence of
H. pylori in natural waters (Hegarty et al., 1999; ; Sasaki et al., 1999; Horiuchi et al., 2001;
Moreno et al., 2003; Benson et al., 2004). As well, in the laboratory, H. pylori has been shown to
survive for days, up to weeks, in sterile river water, stream water, saline solution, and distilled
water at a wide variety of pH levels and in temperatures ranging from 4°C to 25°C (West et al.,
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1992; Shahamat et al., 1993; Adams et al., 2003; Azevedo et al., 2008). As with Legionella and
mycobacteria, evidence has been supplied that biofilms and free-living waterborne amoebae may
provide environmental niches where H. pylori can persist (Park et al., 2001; Winiecka-Krusnell et
al., 2002; Watson et al., 2004; Braganca et al., 2007)
Waterborne transmission has been suggested as an important source of infection in
developing countries (Bellack et al., 2006). Supporting evidence has come from epidemiological
studies showing that individuals consuming untreated or more-contaminated waters had a high
risk of infection (Klein et al, 1991; Goodmane et al, 1996; McKeown et al., 1999; Herbarth et al.,
2001; Brown, 2002). There has been less evidence of the importance of waterborne transmission
in developed countries (Percival and Thomas, 2009). However, findings of H. pylori in drinking
water distribution systems suggest it still can play an important role (Baker and Hegarty, 2001;
Watson et al., 2004; Giao et al., 2008; Percival and Thomas, 2009). Additional research is
required to provide further insight into the persistence, viability and associated risk of H. pylori
in drinking water systems.
The infectious dose necessary for colonization of humans is not known. Results of
challenge studies suggest that it is less that 104 cells, and related to stomach pH (Solnick et al.,
2001; Graham et al., 2004). However, given the high percentage of infected individuals among
the population and the evidence from cases of accidental infection (e.g., from laboratory work,
use of improperly maintained endoscopes), the dose could be much lower (Langenberg, 1990;
Matysiak-Budnik et al., 1995).
B.2.4.2 Health effects
Human infection with H. pylori leads to gastritis, or inflammation of the stomach lining
(Dunn et al., 1997; Kusters et al., 2006). The organism colonizes the human stomach, stimulating
the immune system and inflammatory cells; and it is this response that brings about gastritis. In
the majority of H. pylori infections there are no outward telltale signs of disease (Kusters et al.,
2006). It has been well established that infections with H. pylori are generally acquired during
childhood, with a lower frequency of infection in adults (Allaker et al., 2002; Ernst and Gold,
2006). Further, infection, once established is considered to be lifelong unless treatment is pursued
(Blaser et al., 1992; Kusters et al., 2006). Broad estimates of the risk of infected persons
developing these advanced diseases have been put at 10-20% for peptic ulcer disease and 1-2%
for gastric cancer (Ernst and Gold, 2000; Kusters et al., 2006). H. pylori is also the primary cause
of peptic ulcers (Kuipers et al., 1995). It has been estimated that 85-95% of ulcers are the result
of infection with this organism (Kuipers et al., 1995). Carriage of H. pylori has also been
recognized as an important risk factor for the development of gastric cancer (i.e., gastric
lymphoma and adenocarcinoma) (Dunn et al., 1997; Pinto-Santini et al., 2005).
Infection with H. pylori is treatable (Scott et al., 1998; Vakil et al., 2007); and researchers
have indicated that data from animal and human infection studies suggests that an H. pylori
vaccine is possible (Graham et al., 2004; Del Guidice et al., 2009). This area of research is
currently being explored.
B.2.4.3 Treatment technology
Similar to other bacteria, a proportion of the H. pylori present in the source water will be
removed using physical methods, such as coagulation, sedimentation, and filtration. H. pylori is
also susceptible to disinfectants commonly used in drinking water treatment (e.g., chlorine, UV,
ozone and monochloramine)
Literature regarding the disinfection of H. pylori is limited when compared to that
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available for other waterborne bacterial pathogens. Investigations have been made difficult due to
the fact that cells of H. pylori become viable but non-culturable in the environment, and this form
cannot be detected easily by regular culture methods (Moreno et al., 2007). With chlorination,
data provided from the few reported studies suggested log reductions of culturable H. pylori cells
ranging from 0.3 log at 0.1 mg/L chlorine for 1 minute (Baker et al., 2002) to greater than 4 log at
0.5 mg/L chlorine for 80 seconds (Johnson et al., 1997), to approximately 7 log at 1 mg/L
chlorine for 5 minutes (Moreno et al., 2007). Moreno et al (2007) conducted research using a
combination of direct viable count and fluorescent in-situ DNA hybridization methods (DVCFISH) specifically to study the effects of chlorination on H. pylori cell viability. The researchers
demonstrated that viable H. pylori cells could be detected after 3 hours of exposure to 1.0 mg/L
chlorine, but not after 24 hours of exposure. For UV disinfection, Hayes et al. (2006) reported
greater than 4 log inactivation of culturable H. pylori cells at fluences of less than 8 mJ/cm2.
Disinfectant CT99 values for H. pylori reported by Baker et al. (2002) were ozone: 0.24 mg/L
min; chlorine: 0.299 mg/L min; and monochloramine 9.5 mg/L min. In terms of response to
disinfection as compared to E. coli, Baker et al. (2002) reported that H. pylori was statistically
more resistant to chlorine and ozone, but not to monochloramine. Other authors have similarly
reported H. pylori having greater resistance to chlorine as compared to E. coli (Johnson et al.,
1997; Moreno et al., 2007).
Association with biofilms has also been shown to protect H. pylori from disinfectants,
similar to other bacterial pathogens. Giao et al. (2010) observed H. pylori cells (measured by
peptide nucleic acid [PNA] probe) remained viable for at least 26 days following exposure to
0.2 and 1.2 mg/L chlorine. Also, in contrast to findings provided by other researchers, the authors
observed that H. pylori cells in suspension did not lose culturability after 30 minutes exposure to
chlorine at an initial concentration of 1.2 mg/L (Giao et al., 2010). The current body of research
suggests that the CT provided by a typical water treatment plant is sufficient to inactivate H.
pylori in the finished water. However, if H. pylori does enter the distribution system, potentially
through a break in treatment or infiltration into the system, disinfectant residuals maintained in
the distribution system are probably insufficient for inactivation (Baker et al., 2002). Successful
distribution system control of Helicobacter would similarly be aided by management steps to
reduce the biofilm formation and the presence of free-living amoebae in this environment.
B.2.4.4 Assessment
Overall, the predominant transmission route for H. pylori seems to be situation dependent,
with person-to-person transmission playing a key role in many circumstances. Water and food
appear to be of lesser direct importance, but they can still play a significant role in situations with
improper sanitation and lax hygiene
Much is still unknown regarding the ecology and behaviour of H. pylori in water systems.
However sufficient information has been provided to suggest H. pylori can be regarded as a
potential human pathogen with the potential for waterborne transmission. Illness associated with
H. pylori infection is of a mild or benign nature in the majority of cases, and outbreaks of illness
have not been linked to the presence of H. pylori in drinking water supplies. Further research is
needed to provide clarity on such topics as its presence in source waters, its susceptibility to
treatment and disinfection; and its overall significance for drinking water systems in Canada.
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B.3. Issues of Emerging Interest
B.3.1. Disinfection and antibiotic resistance in organisms
Disinfectants and antibiotics exert action on bacteria through very different mechanisms.
Antibiotics characteristically act against specific target sites within the bacteria – interfering with
a particular specific component of an essential process or pathway. In contrast, disinfectants act
in a general manner against multiple targets which are fundamental components of the bacterial
cell (e.g., proteins and DNA/RNA). Free chlorine, chloramine, chlorine dioxide and ozone are all
very strong oxidizers which inactivate bacterial cells by destroying the activity of cell proteins
that can be involved with cell structure or metabolism. UV light inactivates bacterial cells by
altering the DNA in such a way that the cell can no longer multiply. Because of the fundamental
differences in the way these two types of antibacterial strategies operate, antibiotic-resistant
bacteria are not expected to show increased resistance to the action of drinking water
disinfectants.
Bacterial resistance to antibiotics can be brought about in a variety of ways. Some
examples are that cells may not allow the antibiotic to penetrate the cell, they may lack the
required target site, or they or may possess enzymes that can modify or destroy the antibiotic.
There are numerous types of antibiotics which can be categorized into different classes based on
their structure or mode of action. Bacteria having a particular resistance mechanism may be
unaffected by antibiotics of a similar class or that target the same site. These same bacteria may
be vulnerable to different antibiotics, or may possess mechanisms that make them resistant to
multiple classes of antibiotics.
Very little data has been generated to date regarding the effects of disinfectants on
antibiotic-resistant bacteria in drinking water. Some early work found that a greater proportion of
heterotrophic plate count bacteria in treated water are antibiotic-resistant bacteria as compared to
those in untreated water (Armstrong et al., 1981; 1982). Templeton et al., (2009) conducted an
investigation on the susceptibility of ampicillin and trimethoprim-resistant strains of E. coli to
free chlorine and UV disinfection. The authors observed no differences in UV inactivation
between antibiotic-resistant and antibiotic-sensitive E. coli under the doses and contact times
tested. The trimethoprim-resistant E. coli strain did show slightly greater resistance to free
chlorine than antibiotic-sensitive E. coli; however the authors concluded that the difference was
likely to be negligible under chlorine doses and contact times typically observed in routine
drinking water treatment. It was further concluded that these disinfectants did not likely select for
ampicillin or trimethoprim resistance during drinking water treatment. No drinking water studies
were found pertaining to the inactivation rates for other disinfectants such as ozone or chlorine
dioxide against antibiotic-resistant bacteria.
Presently there is no evidence to indicate that the use of disinfectants in drinking water
systems favours the selection of antibiotic-resistant bacteria in any way (Templeton et al., 2009).
Additional study in this area is needed. The evidence at present, though limited, suggests that
antibiotic resistance in bacteria is not an important factor in chlorine and UV treatment
effectiveness at doses and contact times typically applied in drinking water treatment systems.
B.3.2. Residential-scale and private drinking water systems
The presence of E. coli in a residential-scale or private drinking water system
demonstrates that the source or the system has been impacted by recent faecal contamination; as a
result, the water is unsafe to drink. The absence of E. coli during routine verification should be an
27
Guidance on waterborne bacterial pathogens
For Public Consultation
adequate indication of the sufficient removal and inactivation of enteric bacterial pathogens.
Where applicable, testing frequencies for residential-scale 1 systems will be determined by the
responsible authority and should include times when the risk of contamination is greatest, for
example, in early spring after the thaw, after an extended dry spell, or following heavy rains. For
owners of private supplies, existing wells should be tested two to three times per year and during
these same periods. New or rehabilitated wells should also be tested before use to confirm
microbiological safety.
Other bacterial pathogens that occur naturally in the water environment can be found in
groundwater, though typically at a lower frequency and in lower numbers than in surface waters.
The levels of these organisms necessary to cause disease in healthy individuals are uncertain,
though limited study has suggested that reasonably elevated numbers beyond those typically
found in source waters are required. These organisms are most likely to be found in distribution
system biofilms, and can survive and grow there to reach significant populations. In smaller
systems, distribution system biofilms are less of a concern than in municipal systems because
distribution systems are smaller or non-existent and the retention time for the finished water is
shorter. Nevertheless, private homeowners should also be aware that in the case of Legionella,
domestic hot water systems have been identified as being contaminated with this organism and as
a result should keep the water heater at a suitable temperature (60ºC) to protect against the
potential for the growth of this organism. The National Plumbing Code of Canada includes
requirements of a minimum of 60°C for water temperature in hot water storage tanks, to address
the growth of Legionella (NRCC, 2010). Homeowners should also take appropriate safety
measures to reduce the risk of scalding at the tap. These measures include installing thermostatic
or pressure-balanced mixing valves to control the water temperature at the tap (Bartram et al.,
2007; Bentham et al., 2007).
B.3.3. Point of entry and point of use treatment devices.
The information on treatment, disinfection and inactivation of the organisms in this
document is more relevant to municipal-scale systems. Municipal treatment of drinking water is
designed to reduce microbial contaminants to levels below typically shown to be associated with
disease. The use of residential-scale treatment devices on municipally treated water is generally
not necessary but primarily based on individual choice. In cases where small systems or
individual households obtain drinking water from private wells or surface water supplies such as
lakes, treatment devices can be used as an additional barrier for reducing pathogen concentrations
in drinking water.
Point of entry systems (installed where water enters the home) and point of use systems
(installed at the faucet) have received interest for use in treatment and disinfection of drinking
water in small, rural or remote communities, particularly those using a groundwater source. The
most common types of treatment devices available for the removal and inactivation of waterborne
pathogens (including bacteria) are UV disinfection and membrane filtration (reverse osmosis,
nanofiltration). These technologies have been shown to effectively remove waterborne pathogens
from drinking water (LeChevallier and Au, 2004; MWH, 2005).
1
For the purposes of this document, a residential-scale water supply system is defined as a system with a minimal or
no distribution system that provides water to the public from a facility not connected to a municipal supply.
Examples of such facilities include schools, personal care homes, day care centres, hospitals, community wells,
hotels, and restaurants. The definition of a residential-scale supply may vary between jurisdictions.
28
Guidance on waterborne bacterial pathogens
For Public Consultation
Health Canada does not recommend specific brands of treatment devices, but it strongly
recommends that consumers use devices that have been certified by an accredited certification
body as meeting the appropriate NSF International (NSF)/American National Standards Institute
(ANSI) drinking water treatment unit standards. Homeowners should ensure that the selection
and installation of treatment devices comply with applicable local regulations. Homeowners
should also follow the proper procedures for operation and maintenance found in the
manufacturer’s instructions. These instructions should be consulted regarding the device’s
performance capabilities.
29
Guidance on waterborne bacterial pathogens
For Public Consultation
Part C. References and acronyms
C.1
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Guidance on waterborne bacterial pathogens
C.2
For Public Consultation
List of acronyms
AIDS
ANSI
AWWA
CCL
CDC
CFU
CT
DAEC
DNA
EAEC
EHEC
EIEC
EPA
EPEC
ETEC
HIV
HPC
LP
Mac
MP
NSF
NTU
PCR
PHAC
POE
POU
RNA
UV
VNC
WHO
acquired immune deficiency syndrome
American National Standards Institute
American Water Works Association
Contaminant Candidate List
Centers for Disease Control
colony-forming unit
concentration × time
diffuse adherent E. coli
desoxyribonucleic acid
enteroaggregative E. coli
enterohaemorrhagic E. coli
enteroinvasive E. coli
Environmental Protection Agency (United States)
enteropathogenic E. coli
enterotoxigenic E. coli
human immunodeficiency virus
heterotrophic plate count
low pressure
Mycobacterium avium complex
medium pressure
NSF International
nephelometric turbidity units
polymerase chain reaction
Public Health Agency of Canada
point of entry
point of use
ribonucleic acid
ultraviolet
viable-non-culturable
World Health Organization
53
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