Page 10: Guidelines for Canadian Recreational Water Quality – Third Edition
Part II: Guideline Technical Documentation
No guideline values can be established for waterborne pathogenic microorganisms in recreational waters. Testing for their presence in waters used for recreation should be performed only when there is epidemiological or other evidence to suggest that this is necessary.
There are three main types of pathogenic microorganisms that can be found in recreational waters: bacteria, viruses and protozoa. Many occur as a result of contamination from human or animal wastes, whereas some are free-living microorganisms that exist naturally in the recreational water environment.
The challenges associated with the detection of pathogenic microorganisms in recreational waters are currently too great to recommend this practice as part of a regular monitoring program. Surveillance should be undertaken only during special circumstances, such as during waterborne disease outbreak investigations.
Faecal indicators such as E. coli and enterococci are the best available surrogates for predicting the presence of enteric pathogenic microorganisms. The presence of these indicators is expected to indicate the possible presence of these organisms. The absence of the recommended faecal indicators, however, should not be interpreted to mean that all pathogenic microorganisms are also absent. Although it is not possible to completely eliminate the risk of waterborne disease, adopting a multi-barrier approach to recreational water management will help minimize the risk of human exposure to pathogenic microorganisms (bacteria, viruses and protozoa) in recreational waters.
Information is provided on those pathogens recognized as having significance for Canadian recreational waters. This list is not intended to be exhaustive, and responsible authorities may wish to provide information on other organisms to consider regional interests. Additional information on many of these organisms can be found in the technical documents for the Guidelines for Canadian Drinking Water Quality.
A number of pathogenic bacteria can potentially be found in Canadian recreational waters. Enteric pathogenic bacteria occur in recreational waters as a result of contamination with human or animal faecal wastes. Sources include sewage discharges, combined sewer overflows, stormwater, malfunctioning septic waste systems and infected swimmers. A number are recognized zoonotic pathogens, and thus faecal shedding by animals and stormwater runoff from areas affected by the presence of animals are also important sources. Transmission occurs via the faecal-oral route, through accidental ingestion of contaminated waters. Gastrointestinal symptoms are the most common manifestation of illness following infection with enteric bacterial pathogens. Some pathogens can cause illness with more serious outcomes. E. coli and enterococci are the best available indicators for predicting the possible presence of enteric pathogenic bacteria.
Other pathogenic bacteria can be free-living species or can enter natural waters through means other than faecal contamination. Transmission can occur in waters containing sufficient quantities of the organisms, typically by inhalation or via direct contact with body surfaces. The types of illness caused can be varied, ranging from respiratory illnesses to infections of the eyes, ears or skin. As these organisms are not of faecal origin, faecal indicators are not expected to correlate well with the presence of these bacteria. Currently, there is no recognized microbiological indicator for many of these pathogens.
Campylobacter species are Gram-negative, motile, non-spore-forming, spiral, curved or S-shaped rods. They are thermophilic (growing optimally at 42°C and incapable of growth below 30°C) and mesoaerophilic (surviving best under partially anaerobic conditions) organisms. The genus Campylobacter is composed of 15 species; however, C. jejuni and C. coli represent the major species of human concern in the water environment.
Campylobacter are predominantly considered to be zoonotic pathogens (Fricker, 2006). The organisms are harboured in the intestinal tract of a wide range of domestic and wild animals, particularly birds. Poultry is regarded as the primary avian source, and the organism has been isolated from virtually all bird species (Fricker, 2006). It is likely that a significant proportion of seagulls also carry these organisms (Moore et al., 2002; Pond, 2005). Cattle, sheep and pigs are also considered to be reservoirs.
The exact mechanisms of Campylobacter virulence are incompletely understood. Attachment to and invasion of the human intestinal tract are important factors in causing disease. C. jejuni is reported to be capable of producing a cholera-like enterotoxin that is thought to illicit the production of a profuse, watery diarrhoea in ill individuals.
Symptoms of Campylobacter enteritis include a profuse, watery diarrhoea (with or without blood and/or faecal leukocytes), cramps, abdominal pain, chills and fever. The average incubation period is 2-3 days but can span from 1 to 8 days (Percival et al., 2004). Illness is typically self-limited, requiring 3-7 days for recovery. Estimates of the number of cells generally required to be ingested to lead to infection have ranged from as many as 104 organisms to as few as 500-1000 cells (Percival et al., 2004; Pond, 2005). With pathogens in general, it is theorized that a single organism is sufficient to cause human infection. Epidemiological studies have shown, however, that the dose required is usually greater.
Certain complications (Guillain-Barré syndrome, Reiter's syndrome, appendicitis, carditis and meningitis) have been associated with Campylobacter enteritis; however, these are considered rare. Fatalities from Campylobacter infection are uncommon and have been predominantly restricted to infants, the elderly or patients afflicted with other underlying illness (Pond, 2005).
Despite the fact that Campylobacter spp. can be fairly widely isolated from surface waters, there have been virtually no recorded instances of Campylobacter-associated illness as a result of recreational water activity in North America. The U.S. CDC reported that Campylobacter spp. were not implicated as the causative agents in any of the recreational water outbreaks of gastroenteritis to have been documented in the United States for the period 1992-2002 (Craun et al., 2005). Similarly, no outbreaks of campylobacteriosis have been recorded in Canadian recreational waters.
Pathogenic E. coli
E. coli are Gram-negative, motile, facultatively anaerobic, non-spore-forming rods that are natural inhabitants of the intestinal tract of humans and animals. The vast majority of the E. coli isolates are harmless; however, there are several serotypes or strains that possess virulence factors enabling them to act as human pathogens. Pathogenic enteric strains can be separated into six groupings according to their serological or virulence characteristics: enterohaemorrhagic (EHEC), enterotoxigenic (ETEC), enteroinvasive (EIEC), enteropathogenic (EPEC), enteroaggregative (EAEC) and diffuse adherent (DAEC). Human sewage is the principal source of all of the major pathogenic E. coli groups, with the exception of EHEC. Cattle are considered the primary reservoir for EHEC, although human wastes also remain an important source.
Of the groupings, it is the EHEC group--(also commonly referred to as verocytotoxigenic E. coli [VTEC] or Shiga-toxin producing E. coli [STEC])--that is of greatest importance to recreational waters. E. coli O157:H7 is the most significant serotype of this group, and has been identified as the causative agent in a number of recreational water outbreaks (Craun et al., 2005).
An important virulence factor for EHEC is this ability to produce Shiga-like toxins, similar to those produced by Shigella dysenteriae. EHEC infection causes haemorrhagic colitis, marked by grossly bloody diarrhoea, severe cramping and abdominal pain with a general lack of fever. The incubation period for the disease ranges from 1 to 8 days (Percival et al., 2004; Pond, 2005), with the duration of infection lasting from 1 to 12 days (Percival et al., 2004). Persons only suffering from diarrhoea typically experience a full recovery (Pond, 2005). An estimated 2-8% of all cases progress to what is known as haemolytic uraemic syndrome, or HUS--a life-threatening condition involving large-scale destruction of red blood cells and kidney failure. Children, the elderly and immunocompromised persons are at increased risk for developing HUS.
The number of EHEC cells needed to be ingested in order to lead to infection is considered to be very low. General estimates regarding the infectivity of E. coli O157:H7 suggest that ingestion of fewer than 100 cells may be all that is necessary (Percival et al., 2004), and that as few as 50 or even 5 organisms may be sufficient (Pond, 2005).
According to surveillance data published by the U.S. CDC for the period 1992-2002, EHEC were associated with 25% (16 of 64) of the total number of outbreaks of gastrointestinal illness reported for natural waters (Moore et al., 1993; Kramer et al., 1996; Levy et al., 1998; Barwick et al., 2000; Lee et al., 2002; Yoder et al., 2004). E. coli O157:H7 was the serotype implicated in 14 of 16 of those outbreaks. The remaining two outbreaks involved E. coli serotypes O121:H19 and O26:NM.
In August 2001, an outbreak of E. coli O157:H7-associated illness involving four children was linked to swimming at a public beach in Montreal (Bruneau et al., 2004). This was the first reported incident of E. coli O157:H7 to be associated with recreational water activity in Canada. Weekly water samples collected around the time of the outbreak were shown to be within the recreational water quality limits specified by the Province of Quebec. It was suggested that a high swimmer population and the shallow depth of water encountered in the swimming area contributed to the transmission of the organisms. To date, there have been no reported fatalities resulting from infection with pathogenic E. coli acquired through recreational contact with natural waters in either the United States or Canada.
Salmonella are members of the family Enterobacteriaceae. They are Gram-negative, facultatively anaerobic, motile, non-spore-forming rods. The taxonomy of the genus Salmonella is quite complex. Currently, there are over 2500 known Salmonella serotypes (or serovars) (Lightfoot, 2004). The genus is officially thought to comprise two species: S. enterica and S. bongori (Percival et al., 2004). S. enterica can be further subdivided into six subspecies (S. enterica subsp.): enterica, salmae, arizonae, diarizonae, houtenae and indica. The majority of the serotypes encountered in cases of human gastroenteritis belong to the subspecies S. enterica subsp. enterica (Lightfoot, 2004). Owing to the complexity of the nomenclature, by convention, when referring to Salmonella, the serotype is adopted in place of the species name. Thus, S. Enteritidis takes the place of S. enterica subsp. enterica serovar enteritidis.
With the exception of the typhoidal species (S. Typhi, S. Paratyphi), Salmonella are considered zoonotic pathogens. Reservoirs for non-typhoidal Salmonella species include poultry, swine, birds, cattle, rodents, tortoises and turtles, dogs and cats (Percival et al., 2004). Humans recovering from illness can also provide a source of Salmonella, and asymptomatic infections among humans are also possible. In contrast, humans are considered the primary source of S. Typhi and S. Paratyphi. Occurrence of these isolates in animal hosts or in the natural environment is rare, particularly in Canada.
Gastroenteritis represents by far the most commonly encountered type of Salmonella-associated illness. The chief symptoms are mild to severe diarrhoea, nausea and vomiting. Symptoms usually appear between 12 and 48 hours from the time of infection, but this time lag may be reduced in cases where large quantities of cells have been consumed (Percival et al., 2004). Illness is generally mild and self-limiting, lasting 2-5 days on average. Reports on the infectivity of Salmonella have suggested that the median dose for the non-typhoidal species may be as low as 1000 cells, and possibly below 10 cells (Hunter, 1997; Pond, 2005).
Enteric fever (typhoid or paratyphoid fever) is a more severe and often fatal form of salmonellosis caused by S. Typhi and S. Paratyphi. Symptoms of the illness are prolonged fever, diarrhoea and abdominal pain; progression to septicaemia may also occur. Waterborne outbreaks of enteric fever are more prevalent in developing countries where crowded living conditions and poor hygienic practices exist and are often associated with improperly treated drinking water supplies. Cases are rare in North America.
Septicaemia represents the condition in which the infecting bacteria have invaded the bloodstream and is accompanied by visible symptoms, such as high, remittent fever. Fatal damage to the liver, spleen, respiratory or neurological functions may occur when the organism has spread to these organs or systems. Septicaemia from non-typhoidal species is uncommon (Pond, 2005).
Although Salmonella can be fairly widely isolated from surface waters, there have been no recorded outbreaks from Salmonella as a result of recreational water activity in North America. U.S. CDC surveillance data for the years 1992-2002 indicated that Salmonella was not cited as a causative agent for any of the waterborne outbreaks of gastroenteritis reported over that period. Surveillance in Canada has been somewhat limited; however, similarly, there have been no documented outbreaks from Salmonella in Canadian recreational waters.
Shigella species are members of the family Enterobacteriaceae and, as such, possess many of the same characteristics as E. coli. Both are Gram-negative, facultatively anaerobic, non-spore-forming rods. Unlike the majority of E. coli isolates, however, Shigella species do possess certain attributes that make them important human pathogens. The genus Shigella is composed of four species: S. sonnei (1 serotype), S. flexneri (6 serotypes), S. boydii (15 serotypes) and S. dysenteriae (10 known serotypes). Two species, S. sonnei and S. flexneri, account for the vast majority of Shigella-associated illness in North America (CDC, 2005a). Other Shigella species are uncommon, but remain important causes of disease in developing countries (CDC, 2005a).
Humans are considered to be the only important reservoir for Shigella (Percival et al., 2004). Non-infected individuals are not expected to harbour the organism. Recovering individuals may continue to shed significant numbers of the bacterium for several weeks after symptoms have resolved, and asymptomatic carriage of Shigella is also possible. Municipal sewage discharges present an obvious source of Shigella; however, faecal shedding by infected swimmers may be the most significant source of the organism in recreational waters (Kramer et al., 1996; Levy et al., 1998).
Shigella causes what had been historically referred to as bacillary dysentery (invasion of the intestinal tract, causing frequent passage of stools containing blood and mucus). Illness (shigellosis) is caused by invasion and colonization of the intestinal tract, which leads to inflammation and the destruction of intestinal epithelial cells. Shigella species are also capable of producing a heat-labile enterotoxin; however, its role is not completely understood (Percival et al., 2004).
Shigellosis is characterized by watery or bloody diarrhoea, abdominal pain and fever. Symptoms often present within 1-3 days post-infection, but may be evident in as little as 12 hours. The severity of illness is strongly dependent on the virulence of the individual species or strain. S. sonnei infections are thought to be both of shorter duration and somewhat milder than those caused by S. flexneri (Percival et al., 2004). In many developing countries, S. dysenteriae is known to be responsible for causing severe epidemics. S. dysenteriae serotype 1 is also known to be capable of producing what is referred to as Shiga toxin--a unique toxin (separate from the general Shigella enterotoxin) that can be extremely damaging to human intestinal and kidney endothelial cells. For S. sonnei or S. flexneri, an inoculum of 100 cells may be sufficient to produce infection, whereas S. dysenteriae may require the ingestion of as few as 10 cells to initiate disease (Pond, 2005).
In North America, most cases of shigellosis are mild and self-limiting. Infection typically does not spread beyond the intestinal tract. Complications such as Reiter's syndrome and HUS (following infection with S. dysenteriae serotype 1) have been reported, but are uncommon. Similarly, mortality is rare, but higher incidences may be observed among the elderly and in undernourished children (Pond, 2005).
According to CDC surveillance data, Shigella accounted for approximately 22% (14 of 64) of the total number of outbreaks of gastrointestinal illness reported for natural recreational waters in the United States over the period 1992-2002 (Moore et al., 1993; Kramer et al., 1996; Levy et al., 1998; Barwick et al., 2000; Lee et al., 2002; Yoder et al., 2004). S. sonnei was implicated as the causative agent in all but one of these incidences. Recreational lakes provided the setting for the majority of the outbreaks reported, with poor water circulation frequently cited as a contributing factor. It was suspected that faecal contamination by other swimmers was the cause in the majority of these instances. Given the high infectivity reported for Shigella, it is thought that accidental swallowing of water containing relatively low concentrations of these organisms may be sufficient to cause illness.
Although surveillance has been somewhat limited, to date there have been no reported incidences of Shigella-associated illness as a result of recreational water activity in Canadian waters.
Aeromonas are Gram-negative, facultatively anaerobic, variably motile, oxidase-positive, rod-shaped to coccoid-like bacteria. They are thought to share many morphological and biochemical characteristics with members of the Enterobacteriaceae family, which includes E. coli.
Currently, the genus Aeromonas is thought to consist of 17 unique genospecies and 14 unique phenospecies (Moyer, 2006; U.S. EPA, 2006a). The genus may be subdivided into two major groups: the motile mesophilic species, which grow at temperatures between 15 and 38°C and have been associated with human infections, and the non-motile psychrophilic species, which can grow at temperatures below 15°C and are fish pathogens. At present, six species (A. hydrophila, A. caviae, A. sobria, A. veronii, A jandaei, A. trota and A. schubertii) are recognized as being pathogenic to humans (U.S. EPA, 2006a).
Aeromonas species are natural inhabitants of the aquatic environment. They are frequently found in fresh, marine and estuarine waters, sediments, and sewage and wastewater effluents. Aeromonads are not considered to be present in significant numbers in the faeces of healthy individuals. However, a certain percentage of individuals may carry the organisms in their intestinal tract without showing outward signs of illness.
Aeromonas are recognized animal pathogens and have been isolated from the intestinal tract of a number of animal species, including fish, reptiles, amphibians, birds and domestic livestock, with and without evidence of illness. Occurrence of the organism in recreational waters is not dependent on faecal pollution; however, the organisms are present in high numbers in sewage and thus can be detected at significant levels in sewage-contaminated waters. Aeromonads can grow to relatively high densities in eutrophic waters (Moyer, 2006).
Aeromonas is most often associated with serious wound infections in recreational water users. Infection typically requires the existence of some sort of skin trauma, such as an open wound or following some sort of penetrating injury. Wound infections are characterized by pain, swelling, redness and fluid accumulation around the infected area. Cellulitis (severe inflammation) is frequently observed with such infections, and septicaemia is also considered a fairly common outcome (Percival et al., 2004). Other, rarer complications include necrotizing fasciitis, meningitis, pneumonia, peritonitis and endocarditis (Percival et al., 2004).
Several Aeromonas species (A. hydrophila, A. veronii and A. caviae) have been associated with human gastrointestinal illness. Gastrointestinal illness in humans exposed to contaminated water supplies has been only occasionally reported. Illness is typically mild and self-limiting, although certain strains are reported to be capable of causing a dysentery- or cholera-like illness, marked by severe abdominal cramps, vomiting, diarrhoea (including bloody stools) and fever.
The mechanisms through which Aeromonas is able to cause human illness are not completely understood. The organisms possess a host of virulence factors considered important for infection, colonization and evading the host's immune response. These include both cell-associated mechanisms (pili, flagella, outer membrane proteins, lipopolysaccharides and capsules) and extracellular products (toxins, proteases, haemolysins, adhesions and various hydrolytic enzymes) (U.S. EPA, 2006a).
Marino et al. (1995) reported a positive correlation between A. hydrophila concentrations and skin infections at two swimming beaches in Malaga, Spain. Currently, no evidence has been provided linking Aeromonas concentrations and the risk of acquiring swimming-associated gastroenteritis.
Despite their widespread occurrence, in North America there have been no reported outbreaks of Aeromonas-associated illness as a result of recreational water activities. Superficial infections with Aeromonas are thought to be relatively common; however, Aeromonas infections are not considered reportable illnesses. Thus, an estimate of the likely incidence of Aeromonas infections due to recreational water exposures in Canadian waters is not available.
Legionella are Gram-negative, thermotolerant, motile, short, irregularly shaped bacteria that have strict nutrient requirements when grown on laboratory media. Over 40 species of the genus have been recognized. L. pneumophila (serotype 1) is the species most frequently associated with human disease (legionellosis). It is suspected that all Legionella species may be capable of causing illness, and approximately half of the identified species have been implicated in human disease (Hall, 2006). Other Legionella species frequently recovered from the environment include L. bozemanii, L. longbeachae, L. dumoffii and L. gormanii.
Legionella are naturally occurring aquatic organisms. They can be isolated from a wide range of freshwater habitats, including soils, lakes, rivers and natural thermal pools at temperatures as high as 60°C. Marine environments typically do not provide appropriate growth conditions for these organisms. Free-living freshwater protozoa such as Naegleria or Acanthamoeba are natural hosts for these organisms. Although Legionella are thought to be fairly resistant to environmental stresses, survival within protozoan hosts is thought to provide an additional, significant measure of protection.
Legionella is typically encountered in low numbers in the aquatic environment, but can reach higher concentrations in sources associated with human-made water supplies, such as cooling towers, air conditioning condensers, humidifiers, hot water tanks, shower heads and whirlpool spas (Percival et al., 2004). Hot springs or other hydrothermal spas are particularly well suited to the survival of Legionella as a result of the elevated water temperatures.
Dose-response experiments with animals have suggested that high doses of Legionella (approximately 107 cells) are required to initiate infection (O'Brien and Bhopal, 1993). In contrast, published reviews of the organism have suggested that the median dose is as low as a few organisms (Percival et al., 2004; Pond, 2005). Aerosol carriage of protozoa that have been heavily parasitized by Legionella may be one means of increasing the number of organisms available to initiate infection (Percival et al., 2004).
Legionella are important agents of respiratory disease in humans. Legionellosis comprises two forms of illness: Legionnaire's disease and Pontiac fever (Pond, 2005). Legionnaire's disease is a more severe and sometimes fatal form of respiratory illness. The disease is defined by the clinical diagnosis of pneumonia, accompanied by microbiological evidence of infection with L. pneumophila or other Legionella species (Pond, 2005). Other symptoms can include fatigue, fever, headache, muscle and/or abdominal pain, jaundice and mental confusion. The incubation period is between 3 and 6 days, and recovery is slow, lasting weeks up to several months. Fatalities can result, largely due to respiratory failure. The mortality rates from community-acquired infections are estimated to be in the range of 5-20% (Pond, 2005).
Pontiac fever is a relatively mild, influenza-like illness, defined by non-pneumonic respiratory illness with microbiological evidence of Legionella infection. The disease has a shorter incubation period (1-2 days), and illness is considered non-fatal, with infected individuals requiring approximately 2-5 days for recovery. It is estimated that Pontiac fever occurs 2-100 times more frequently than Legionnaire's disease (Hall, 2006).
Groups considered most sensitive to Legionella infection include the elderly, immunocompromised individuals, persons with heart or lung disease and individuals who are excessive smokers or consume excess amounts of alcohol.
Despite the fact that Legionella species are thought to be ubiquitous in environmental waters, no recorded outbreaks of legionellosis have been reported in Canada or the United States as a result of recreational activity in natural waters. Any reported outbreaks of legionellosis associated with human recreational water contact have been restricted to treated water facilities, such as hot tubs and spas (Moore et al., 1993; Kramer et al., 1996; Levy et al., 1998; Barwick et al., 2000; Lee et al., 2002; Yoder et al., 2004).
Mycobacterium species are aerobic, non-motile, non-spore-forming, rod- to coccoid-shaped bacteria. The organisms are considered to have a Gram-positive cell structure. However, the mycobacterial cell wall contains high levels of mycolic acid--complex lipids that give the cell surface a waxy, hydrophobic character that resists Gram staining. Positive staining with acid-fast staining techniques is diagnostic for mycobacteria; thus, the organisms are more commonly referred to as "acid-fast."
The pathogenic mycobacteria encountered in recreational waters are environmental species. They are generally referred to as "atypical" or "non-tuberculous" mycobacteria to distinguish them from M. tuberculosis (tuberculosis) and M. leprae (leprosy). Neither M. tuberculosis nor M. leprae is found in the environment. Consequently, they are not a concern for recreational waters. At least 16 different waterborne species have demonstrated the capability for causing infection in humans (Pond, 2005). The species most commonly discussed as having relevance for recreational water exposures are the members of the Mycobacterium avium complex (M. avium and M. intracellulare), which are known to cause respiratory illness; and M. marinum and M. kansaii, which can cause skin infections.
Environmental mycobacteria are considered ubiquitous in natural waters. They can be found in virtually every medium, including soils, wastewater, lakes, rivers, ponds, streams, groundwater and treated water supplies. Few mycobacteria are encountered in marine waters (Pond, 2005; LeChevallier, 2006). The organisms can survive over a wide range of temperatures, extending from below 0°C to above 50°C. Mycobacteria are not known to be present in high numbers in faeces, and sewage is not considered to be a significant source (Falkinham, 2002). M. avium complex members are capable of survival and growth within certain species of phagocytic protozoa, specifically members of the genus Acanthamoeba.
In recreational water environments, transmission can occur through contact with waters containing sufficient quantities of the organisms. The main routes of infection are via inhalation of mycobacteria contained within aerosols and through direct water contact with abraded skin. There is little evidence of person-to-person transmission. Environmental mycobacteria are primarily considered to be opportunistic pathogens, as illness is more commonly observed in individuals with some underlying condition that predisposes them to infection (abraded or traumatized skin; or having a weakened or compromised immune system). Exposures to environmental mycobacteria have been most strongly linked to swimming pool and hot tub use, resulting in cases of skin and soft tissue infections and hypersensitivity pneumonitis (inflammation of the lungs). Recreational contact with natural waters is not considered to be a significant risk factor for acquiring mycobacterial illness.
Although environmental mycobacteria are considered ubiquitous in most types of water, to date there have been no recorded outbreaks of mycobacterial-associated illness through contact with natural recreational waters in either Canada or the United States. The risk of healthy individuals acquiring a mycobacterial infection as a result of recreational activity in natural waters is considered extremely low.
Pseudomonads are Gram-negative, motile, oxidase-positive, non-spore-forming, rod-shaped bacteria. Over 100 species are currently recognized as belonging to the genus Pseudomonas (Hunter, 1997). P. aeruginosa represents the most significant species of human concern.
P. aeruginosa is widely distributed in the aquatic environment and can be frequently isolated from fresh water, seawater and soils (Hunter, 1997). The organism has minimal growth requirements and is able to proliferate in waters of low nutrient content. P. aeruginosa is infrequently isolated from human faeces (Geldreich, 2006). The organism can be recovered from sewage and stormwater (as these contain a mixture of domestic wastes) and from industrial discharges such as food processing and pulp and paper wastes. Swimmers themselves also present another possible source of P. aeruginosa.
Transmission of P. aeruginosa in recreational waters occurs through direct body contact with waters containing sufficient quantities of the organism. Ingestion is not considered to be a significant route of infection.
P. aeruginosa can be responsible for causing skin rashes and eye and ear infections among recreational water users. Infection rarely occurs among healthy individuals unless some condition exists that might predispose them to infection (having a history of ear infections, or reporting frequent immersions) (Hunter, 1997). Ear infections occur when P. aeruginosa is able to enter into and colonize the outer ear canal. Within a few days of swimming, the ear may become itchy and painful, and discharges of pus may be observed. Skin irritations (dermatitis) present as a red, itchy rash, occurring roughly 18-24 hours after water contact. Infection can progress to folliculitis (inflammation of the hair follicles of the skin), which is marked by an increased tenderness of the infected area and the presence of pus-filled blisters or pimples that surround the hair follicles.
Several epidemiological studies have demonstrated the existence of a link between Pseudomonas in natural waters and the incidence of eye and skin infections among swimmers (Seyfried and Cook, 1984; Springer and Shapiro, 1985; Ferley et al., 1989; Marino et al., 1995; van Asperen et al., 1995). Reported outbreaks of Pseudomonas dermatitis have virtually all been associated with treated water venues such as hot tubs, swimming pools or hotel whirlpool or spa baths (Moore et al., 1993; Kramer et al., 1996; Levy et al., 1998; Barwick et al., 2000; Lee et al., 2002; Yoder et al., 2004). The incidence of P. aeruginosa infections from contact with natural recreational waters is not known, as illnesses are usually of mild severity and typically not recorded.
Leptospira are spirochetes--spirally coiled or corkscrew-shaped bacteria. They are Gram-negative staining, aerobic, long, thin and motile organisms. Initially, the genus Leptospira consisted of two species, the pathogenic L. interrogans and the free-living L. biflexa (WHO, 2003b). At present, 12 Leptospira species are recognized, and over 200 pathogenic serotypes have been described, in which the more severe forms are attributed to serovars of L. interrogans (Pond, 2005). By convention, the serotype name is often adopted as the species name when referring to specific strains.
Leptospira species can be either pathogenic or free-living. They are encountered worldwide and are predominantly associated with freshwater environments. The pathogenic leptospires are important zoonotic pathogens that are carried in the renal tract (kidney) of infected animal carriers and excreted in the urine. Small rodents, such as rats, mice and voles, are considered the most important source of pathogenic Leptospira. The organisms can also be spread by domestic animals, such as cattle, pigs, dogs and cats, sheep, goats and horses (WHO, 2003b; CDC, 2005b). Heavy rainfall is thought to facilitate the spread of the organisms, as runoff from contaminated soils can affect surface waters (Pond, 2005).
Human infection can occur following direct contact with the urine of infected animals or indirectly though contact with contaminated water, soil or mud. Leptospires gain access through cuts or abrasions in the skin or via passage through the mucous membranes of the eyes, nose and mouth. Ingestion of contaminated water and inhalation of leptospires carried in aerosols are also possible routes of infection. It is thought that ingestion of as few as 1-10 organisms can be sufficient to lead to human illness (Pond, 2005). Recreational water activity is perhaps the most significant source of exposure for acquiring illness, although swimming-associated outbreaks are considered extremely rare (Pond, 2005).
Illness following infection with Leptospira can range in severity from a mild, influenza-like illness to more severe, and possibly fatal, disease. Early symptoms of illness are fever, chills, headache, muscle pains, vomiting and reddening of the eyes (Public Health Agency of Canada, 2004). Recovery from mild illness is usually complete, but can be lengthy, in some cases requiring months to years (WHO, 2003b). If left untreated, the disease can progress to more serious illness. Severe cases of leptospirosis can be fatal, with death occurring as a result of kidney failure, cardiorespiratory failure or extensive haemorrhaging. The reasons for the differences in the severity of infection are not fully understood; however, it is believed that each pathogenic serovar possesses the capacity to cause either mild or severe disease (WHO, 2003b).
Illness can be difficult to diagnose, as it may be mistaken for other infections or illnesses that produce similar symptoms. Similarly, mild forms of the illness may not always be reported.
Leptospirosis is considered to be a greater concern among developing countries and in tropical climates. There have been three reported outbreaks of leptospirosis in recreational waters in the United States over the period 1991-2002 (Moore et al., 1993; Barwick et al., 2000; Lee et al., 2002).
Reports of increases in the number of observed cases of leptospirosis in developed countries suggest that Leptospira may represent an important re-emerging pathogen (CRC, 2004; Meites et al., 2004). Currently, the prevalence of Leptospira in Canadian waters is not known. To date, there have been no documented incidences of Leptospira infection from recreational water activity in Canadian waters.
Members of the genus Staphylococcus are Gram-positive, catalase-positive, non-motile cocci. S. aureus is considered the major pathogen of the genus and is the species of most significance for recreational water users.
S. aureus is not considered to be a natural inhabitant of environmental waters. The major reservoirs for this organism are the skin, nose, ears and mucous membranes of warm-blooded animals. The presence of S. aureus in recreational waters is predominantly due to releases of the organism from the mouths, noses and throats of swimmers and from discharges from existing infections. The organism can be isolated from human faeces; however, occurrence is thought to be variable (Percival et al., 2004). Sewage and stormwater are additional sources of the organism.
Transmission of S. aureus in recreational waters occurs via direct contact with waters containing sufficient quantities of the organism. Infection occurs through cuts or scratches on the skin or, to a lesser extent, through contact with the eyes and ears. Person-to-person spread of the organism is also possible. Ingestion is not considered to be a significant route of exposure. The organism produces a wide array of extracellular toxins, exoenzymes and adherence factors that are used during colonization and infection and for evading host immune defences (Percival et al., 2004). Concentrations of a few hundred cells per millilitre may be sufficient to initiate infection in injured or distressed skin (Percival et al., 2004).
S. aureus is predominantly associated with skin infections in recreational water users. Common infections include infected cuts and scratches, boils, pustules, dermatitis, folliculitis and impetigo (WHO, 2006). Infections are most often pus-forming, with symptoms often not becoming apparent until 48 hours after contact. Other illnesses to which the organism has been linked include eye infections, otitis externa and urinary tract infections (WHO, 2006).
Epidemiological investigations have demonstrated evidence of possible connections between the presence of staphylococci in recreational waters and swimmer illness (Calderon et al., 1991; Charoenca and Fujioka, 1995). However, to date, there has been no conclusive evidence relating the frequency of illness to the concentration of S. aureus in recreational waters. In certain instances, testing may provide additional information--for example, in assessing the effects of high swimmer densities on water quality and the potential implications for the possible person-to-person transfer of pathogens.
Viruses are submicroscopic organisms, much smaller in size than bacteria. They are simply constructed, consisting of a nucleic acid core composed of either RNA or DNA, and surrounded by an external protein shell called a capsid. The nucleic acid encodes for viral structural proteins and enzymes necessary for replication, whereas the capsid protects the viral unit from environmental stresses. Some viruses (enveloped viruses) may also possess a lipoprotein envelope surrounding the capsid. Non-enveloped viruses lack this external layer. Viruses are obligate intracellular parasites and must infect a host cell in order to replicate. As a result, they are incapable of replicating outside of their host environment.
The pathogenic viruses of concern for recreational waters are enteric viruses--viruses that infect the human gastrointestinal tract and are shed in human faeces. These viruses are considered to have a narrow host range, meaning that in general, enteric viruses that infect animals do not infect humans, and vice versa. Transfer to humans in recreational waters occurs via the faecal-oral route through the accidental ingestion of contaminated waters. Some viruses, like the adenoviruses, have additional routes of infection, such as via inhalation or through contact with mucosal membranes of the eyes. Enteric viruses cause a wide variety of human health effects, which can range in severity from mild to severe. Gastrointestinal symptoms (nausea, vomiting, diarrhoea) are the most commonly encountered symptoms of viral illness. Some virus infections can result in more serious health outcomes, although these are considered to be much rarer.
There are over 100 types of viruses that can be excreted in faeces and thus can potentially be transmitted to recreational waters. The viruses most commonly associated with waterborne illness include adenoviruses, astroviruses, enteroviruses (polioviruses, coxsackieviruses and echoviruses), noroviruses, rotaviruses and the Hepatitis A virus.
Enteroviruses are a large group of small (20-30 nm), non-enveloped RNA viruses belonging to the family Picornaviridae. Members of this group include polioviruses, coxsackieviruses, echoviruses and several yet unclassified enteroviruses. Many enterovirus infections are asymptomatic. The symptoms and severity of illness vary considerably among the individual virus types and serotypes. The most commonly observed health effects are vomiting, diarrhoea, febrile flu-like symptoms, malaise, respiratory disease, headache and muscle ache (Percival et al., 2004). More serious outcomes have been associated with individual virus groups, including myocarditis (coxsackievirus), aseptic meningitis (coxsackievirus, poliovirus), encephalitis (coxsackievirus, echovirus) and poliomyelitis (poliovirus), although these are not considered to be common.
The term "norovirus" has been designated as the official name for the group of viruses formerly known as Norwalk viruses, Norwalk-like viruses or "small, round, structured viruses" (SRSV). Noroviruses are small (27-30 nm), non-enveloped RNA viruses. Norovirus infection is considered to be the leading cause of viral gastroenteritis outbreaks (from all sources) in the United States and the United Kingdom (Percival et al., 2004). The primary symptoms of illness are diarrhoea, vomiting, headache and muscle ache. The onset of projectile vomiting is considered a characteristic trait of norovirus infection. Asymptomatic infections with norovirus are rare. In healthy adults, illness is self-limiting, rarely progressing to more serious concerns (e.g., dehydration). Infection is considered more serious among vulnerable groups such as the elderly.
Rotaviruses are larger (60-80 nm), non-enveloped RNA viruses. Dose-response studies have suggested that rotaviruses are the most infective of all the enteric viruses (Gerba et al., 1996). Rotavirus infection has been implicated as the number one cause of infantile gastroenteritis worldwide. Although all age groups can be affected, infections among healthy adults are often asymptomatic as a result of the immunity acquired during childhood (Percival et al., 2004). Diarrhoea constitutes the predominant symptom of illness, which can become life-threatening should the resulting dehydration and electrolyte imbalance become severe. Groups considered vulnerable for severe disease- and illness-induced mortality include young children, immunocompromised individuals and the elderly.
Adenoviruses are also larger by comparison (70-100 nm) and are non-enveloped DNA viruses. Over 49 individual serotypes have been identified as being capable of causing human illness, with the clinical features and severity of illness varying considerably among the individual types (Percival et al., 2004). The majority of adenovirus serotypes cause respiratory illness, which presents with pharyngitis and cough and cold-like symptoms. Conjunctivitis can also occur as a result of infection of the eye. Gastrointestinal illness, caused exclusively by serotypes 40 and 41, is also a frequently reported outcome. Adenovirus is thought to be second only to rotaviruses as a cause of childhood gastroenteritis (Crabtree et al., 1997). Asymptomatic illness is commonly observed with gastrointestinal infection, as it is believed that the immunity conferred during early childhood is lifelong (Percival et al., 2004).
Hepatitis A virus
The Hepatitis A virus (HAV) is a small (25-28 nm), non-enveloped RNA virus whose major target organ is the liver. The majority of HAV infections are asymptomatic. Illness is most frequently reported among adults. Symptoms include malaise and fever, followed by nausea, vomiting, abdominal pain and, ultimately, jaundice. Infection is typically self-limiting.
Astroviruses are small (28-30 nm), non-enveloped RNA viruses. Of the viral agents known to cause enteric illness, the significance of astroviruses as a cause of waterborne illness is perhaps the least well characterized (Percival et al., 2004). Illness in infected individuals appears similar to rotaviral illness, although markedly less severe.
Occurrence in the environment
Enteric viruses are shed in high numbers in the faeces of infected individuals and can reach concentrations as high as 1010-1012 particles per gram of faeces (Gerba, 2000). Even asymptomatic individuals (those infected, but not exhibiting symptoms of disease) are capable of excreting large numbers of viruses.
The principal route of entry for viruses in recreational waters is via the discharge of sewage-contaminated wastes. Point sources of pollution such as municipal sewage discharges or combined sewer overflows constitute the primary sources of sewage contamination. Non-point sources capable of contributing to the viral loading of environmental waters include storm drains, river discharges (which capture runoff from urban and rural areas) and malfunctioning or improperly designed septic waste systems. Swimmers themselves, particularly young children, can also present a source of contamination through faecal shedding and the accidental release of faecal material. Animal wastes, although capable of harbouring many bacterial and protozoan pathogens, are considered to be of low risk for the transmission of viruses to humans (Cliver and Moe, 2004; Percival et al., 2004). There have been some examples of animals serving as a reservoir for human viruses (avian influenza virus, West Nile virus), yet to date there has been no documented evidence of human waterborne infection having been caused by animal viruses (Cliver and Moe, 2004).
The total viral load of sewage can be quite constant; however, the types and numbers of individual viruses are strongly influenced by the rates of epidemic and endemic illness within the discharging population. As a result, the viral composition of sewage can vary considerably, often demonstrating strong seasonal trends (Krikelis et al., 1985; Tani et al., 1995; Pina et al., 1998; Lipp et al., 2001). Published estimates of culturable viruses in raw sewage suggest that concentrations can reach over 10 000 infectious units per litre (Reynolds et al., 1998; Payment et al., 2001). The presence of viruses in surface waters is expected to vary regionally and is dependent upon (among other factors) the degree and type of faecal contamination and the rates of environmental inactivation. Detectable levels of culturable enteroviruses in surface waters in general have ranged from 1-10/100 L to 1-200/L for more contaminated waters (Pina et al., 1998; Reynolds et al., 1998; Payment et al., 2000; Lipp et al., 2001).
Studies have reported the detection of enteroviruses, noroviruses, rotaviruses, adenoviruses, HAV and astroviruses in marine and fresh waters used for recreational purposes in the United States, Europe and Canada (Payment, 1984; Puig et al., 1994; Pina et al., 1998; Griffin et al., 1999; Chapron et al., 2000; Payment et al., 2000; Schvoerer et al., 2001; Denis-Mize et al., 2004; Jiang and Chu, 2004; Laverick et al., 2004). The studies report varying figures in terms of virus detection frequencies and concentrations. Differences in the analytical methods used in the respective studies prevent direct comparisons of the results; nevertheless, the information provided by these investigations serves to shed some light on the potential vulnerability of recreational waters to contamination with pathogenic viruses.
Viruses are hardy microorganisms that can survive for prolonged periods once shed into the aquatic environment. Survival is dependent upon a number of biological and environmental factors, including the virus's specific physical characteristics, the presence of natural microbial predators and various water characteristics, such as temperature, pH, salinity, turbidity and ultraviolet (UV) levels. Data on the survival of individual virus types in natural waters have been limited. Viruses are generally regarded to be more resistant to environmental degradation than bacteria, and experimental data suggest that some enteric viruses may demonstrate greater resistance than some enteric protozoa (e.g., Giardia) (Johnson et al., 1997).
Surveillance data on recreational water outbreaks published by the U.S. CDC indicated that for the period 1991-2002, 13% (8 of 64) outbreaks of gastroenteritis reported in natural waters were caused by noroviruses (Moore et al., 1993; Kramer et al., 1996; Levy et al., 1998; Barwick et al., 2000; Lee et al., 2002; Yoder et al., 2004). In general, noroviruses were responsible for between 0 and 2 outbreaks per year, with the total number of cases per outbreak ranging from 11 to 168 individuals. Recreational lakes constituted the setting for the majority of the outbreaks, and a 2002 outbreak involving 44 cases at Lake Michigan State Park in Wisconsin was the first documented recreational water outbreak at a Great Lakes beach (Yoder et al., 2004). No other virus types were implicated in any of the other outbreaks reported from 1991 to 2002.
Outbreaks of acute gastroenteritis in which the causative agent could not be identified also regularly constitute a significant proportion of the total number of recreational water-related outbreaks. It is generally suspected that many of these outbreaks are of viral origin. Pathogenic viruses are notoriously difficult to detect, and the short incubation times, range of symptoms encountered and high frequency of illness observed among children are all consistent with viral infections (Cabelli, 1983; Mena et al., 2003; Percival et al., 2004). According to CDC surveillance data, outbreaks of acute gastrointestinal illness of unknown etiology accounted for 23% (14 of 64) documented outbreaks from 1991 to 2002 (Moore et al., 1993; Kramer et al., 1996; Levy et al., 1998; Barwick et al., 2000; Lee et al., 2002; Yoder et al., 2004). Again, freshwater lakes were identified as the most frequent setting for such outbreaks.
Several epidemiological studies have attempted to characterize the relationship between enteroviruses in swimming water and the incidence of recreational water illness (Lightfoot, 1988; Alexander et al., 1992; Fewtrell et al., 1992; van Dijk et al., 1996; Lee et al., 1997; van Asperen et al., 1998; Haile et al., 1999). In general, no significant relationships could be shown between the concentration of enteric viruses and the incidence of swimmer illness. Haile et al. (1999) did observe an increase in the reporting of a number of adverse health effects (vomiting, fever, sore throat and highly credible gastrointestinal illness) on days on which enteroviruses were detected in swimming waters affected by stormwater discharges.
Relationship with indicators
A number of studies have reported a lack of a relationship between the concentration of faecal indicator bacteria and the presence of enteric viruses in recreational waters (Griffin et al., 1999; Schvoerer et al., 2000, 2001; Jiang et al., 2001; Noble and Fuhrman, 2001; Denis-Mize et al., 2004; Jiang and Chu, 2004; Wetz et al., 2004). Pathogenic viruses have been detected in recreational waters at faecal indicator bacteria concentrations below the existing limits for recreational water quality. The reverse has also been true--that waters with indicator counts well above recreational water limits have yielded negative results for the presence of viruses. The lack of a correlation between faecal indicators and enteric viruses is not unexpected, as faecal indicators are present consistently in human and animal wastes and in relatively constant numbers, whereas viruses are specific to human wastes and shedding may be intermittent and seasonal. Viruses are also more resistant than bacteria to environmental stresses and may persist for longer periods. Other organisms have been proposed as potential surrogate indicators (strains of enterovirus, C. perfringens, coliphages and phages of B. fragilis); however, investigations conducted to date have not demonstrated conclusive evidence of a link between these organisms and the detection of viruses in contaminated surface waters (Pina et al., 1998; Griffin et al., 1999, Lipp, 2001; Jiang and Chu, 2004).
Pathogenic protozoa of importance to recreational waters include both enteric and free-living species. Enteric protozoa are common parasites that infect the intestinal tract of humans and other mammals. They are obligate parasites, meaning that they require the infection of a host to replicate and are incapable of growth outside the host environment. The most important stage of their life cycle involves the production of cysts or oocysts that are shed in large numbers in the faeces. These cysts or oocysts are extremely resistant to environmental stresses and can survive for long periods in the environment. Upon ingestion by a new host, the (oo)cysts undergo excystation in the small intestine to initiate infection. These organisms can enter recreational waters as a result of direct or indirect contact with human or animal faeces. Transmission to humans occurs through the accidental ingestion of contaminated waters. The most common manifestations of illness are gastrointestinal symptoms, specifically diarrhoea. E. coli and enterococci are used to indicate faecal contamination and thus the possible presence of these faecal enteric pathogens. Indicator absence does not necessarily indicate that enteric protozoa are also absent.
Free-living protozoa, unlike enteric protozoa, occur naturally in recreational waters and do not require the presence of a host organism to complete their life cycle. Transmission to humans can occur in waters containing sufficient quantities of the organisms through mechanisms such as inhalation or through direct contact with mucous membranes (e.g., those of the eye). The types of illnesses caused by these organisms are varied and include infections of the central nervous system and eye infections. As these organisms are not of faecal origin, faecal indicators are not expected to correlate well with the presence of these protozoans. Currently, there is no recognized microbiological indicator for these pathogens.
The enteric protozoa of most importance to recreational waters are Giardia and Cryptosporidium.
Giardia spp. are small, flagellated protozoan parasites. Species have a two-staged life cycle consisting of a trophozoite (feeding stage) and an environmentally resistant cyst stage. G. duodenalis (syn. lamblia, intestinalis), found in humans and a wide range of other mammals, is the only human-infective species. Other species (G. muris, G. agilis, G. microti, G. psittaci and G. ardea) have been reported in animals, including rodents, birds and amphibians. Molecular characterization of G. duodenalis has demonstrated the existence of genetically distinct genogroups (assemblages) depending on their host range. Some groups have shown occurrence across both human and animal hosts, whereas others have been shown to be host-specific.
Human and animal faeces (especially cattle) are major sources of G. duodenalis. Other recognized animal hosts include beavers, muskrats, dogs, sheep and horses. Many of these animals can be infected with G. duodenalis originating from human sources (Davies and Hibler, 1979; Hewlett et al., 1982; Erlandsen et al., 1988). Epidemiological and molecular data suggest that it is only these human-source strains that have been significantly associated with human illness. The pathogenicity of other, animal-specific G. duodenalis strains and Giardia species is not fully known. As a result, it remains sound practice to consider any Giardia cysts found in water as potentially infectious to humans.
Giardia is commonly encountered in sewage and surface waters. In general, concentrations in wastewater are in the range of 5000-50 000 cysts/L, with surface water concentrations typically ranging from < 1 to 100 cysts/100 L (Medema et al., 2003; Pond et al., 2004).
The exact mechanisms through which Giardia causes illness are not completely understood. Damage to the intestinal mucosa caused by attachment and detachment of the trophozoites contributes to the impairment of intestinal function. The severity of Giardia infection can range from no observable symptoms to severe gastrointestinal illness requiring hospitalization. The most common symptoms of illness include explosive, watery diarrhoea, nausea, intestinal upset, fatigue, low-grade fever and chills.
In theory, a single cyst is sufficient to cause human infection. However, studies have shown that the dose required to cause infection is usually greater. Human (volunteer) feeding studies have suggested that the median dose for infection is around 50 cysts (Hibler et al., 1987), although subjects have shown infection at doses much lower than this (Rendtorff, 1978). The time between ingestion and the excretion of new cysts (prepatent period) ranges between 6 and 16 days. Infection is self-limiting, clearing within 1-3 weeks on average. Some patients may remain as asymptomatic carriers, whereas in other cases individuals may experience recurrent bouts of the disease, a phase persisting for a period of several months to a year. Persistent illness can be treated using a number of antiparasitic drugs.
Cryptosporidium are small, non-motile protozoan parasites. These organisms possess a complex, multi-staged life cycle, of which the most important stage is production of the round, thick-walled oocysts. Sixteen species are currently recognized as belonging to the genus. Two predominant genotypes have been linked to human illness: C. hominis (genotype 1), reported only in humans, and C. parvum (genotype 2), reported in humans, calves and other ruminants. Other species and genotypes have been encountered, but much less frequently.
Humans and cattle are the most significant sources of Cryptosporidium. Sheep, pigs and horses are also considered to be reservoirs (Olson et al., 1997). Rodents are not a significant source of human-infective Cryptosporidium (Roach et al., 1993).
Oocysts are commonly found in water affected by human or livestock wastes by mechanisms such as sewage, swimmer contamination and stormwater runoff. It is suggested that waterfowl (ducks, geese) may be capable of picking up oocysts from their habitat and depositing them elsewhere through discharge in their faeces. Typical concentrations in wastewater are on the order of 1000-10 000 oocysts/L, whereas surface water concentrations in general range from < 1 to 5000 oocysts/100 L (Guy et al., 2003).
The precise means through which Cryptosporidium causes human illness is not fully understood. Damage caused by infection of red blood cells in the mucosa of the small intestine is known to contribute to illness. Cryptosporidium infection can result in illness of varying severity, ranging from asymptomatic carriage to severe, life-threatening illness in immunocompromised individuals. The primary characteristic of illness is profuse, watery and sometimes mucoid diarrhoea. Other symptoms include nausea, vomiting, abdominal pain, weight loss, anorexia and low-grade fever.
For Cryptosporidium, a variety of median infective doses have been reported--although, as is the case with other pathogens, a single organism is theoretically sufficient to initiate infection. Most (volunteer) feeding studies suggest that the median infective dose of Cryptosporidium is between 80 and 140 oocysts (DuPont et al., 1995; Chappell et al., 1999, 2006; Okhuysen et al., 2002). The prepatent period (time between ingestion and the excretion of new cysts) is roughly 4-9 days. Most healthy individuals experience a complete recovery, with the disease resolving itself in about 1-2 weeks. Oocysts may continue to be shed in faeces for a short period following recovery. Currently, there is no effective treatment for cryptosporidiosis in adults. The use of the antimicrobial drug nitazoxamide has been approved by the U.S. Food and Drug Administration for treatment in children (Health Canada, 2012b).
Reported outbreaks of giardiasis and cryptosporidiosis from natural recreational waters have been infrequent. Surveillance data published by the U.S. CDC for the period 1992-2002 indicated that Giardia was responsible for 9% (6 of 64) of the total number of outbreaks of gastroenteritis reported for natural waters (Moore et al., 1993; Kramer et al., 1996; Levy et al., 1998; Barwick et al., 2000; Lee et al., 2002; Yoder et al., 2004). Locations included recreational lakes, a recreational river and a pond setting. Although Giardia has not been linked to outbreaks in natural recreational waters in Canada, it is likely that cases have occurred that were not detected or went unreported.
Surveillance data over the same period indicated that 6 (9%) of the 64 outbreaks of gastrointestinal illness reported in natural waters were caused by Cryptosporidium (Moore et al., 1993; Kramer et al., 1996; Levy et al., 1998; Barwick et al., 2000; Lee et al., 2002; Yoder et al., 2004). Recreational lakes were recorded as the setting for the majority of the outbreaks. A large outbreak at a New Jersey lake in 1994 involving 418 cases was the first recorded U.S. outbreak of cryptosporidiosis related to recreational water use (Kramer et al., 1996). Treated recreational water venues such as water parks and community and motel swimming pools have provided the setting for the majority of outbreaks of cryptosporidiosis. Surveillance in Canada has been limited; to date, however, there have been no reported outbreaks of cryptosporidiosis associated with natural recreational waters. As with Giardia, it is expected that cases have occurred and gone undetected or were not reported.
Relationship with indicators
Although the faecal indicators E. coli and enterococci are good indicators for enteric bacterial pathogens commonly found in natural recreational waters, they have proven to be less effective indicators of protozoan presence. Studies have demonstrated a lack of correlation between concentrations of E. coli and enterococci and the presence of Giardia and Cryptosporidium in surface waters (Hörman et al., 2004; Dorner et al., 2007; Sunderland et al., 2007). E. coli and enterococci are present consistently in human and animal faeces, whereas the presence of Cryptosporidium and Giardia is source dependent. Additionally, shedding of these organisms in the feces of recognized sources can be intermittent and seasonal. Giardia cysts and Cryptosporidium oocysts are also more resistant to stresses than bacteria and may persist in the environment for longer periods.
Other enteric protozoa of potential concern
Other enteric pathogenic protozoa such as Entamoeba and Toxoplasma can be shed in human and animal faeces and thus can conceivably be present to contaminate recreational waters. Currently, there have been no reported outbreaks involving these organisms in recreational waters. Recreational water activity is not considered to be a significant risk factor for illness caused by these organisms.
The free-living protozoa recognized as the most important in natural recreational waters are Naegleria and Acanthamoeba.
Naegleria are small, thermophilic, free-living freshwater amoebae. The genus Naegleria is composed of six species. N. fowleri is the primary human pathogen and the species of concern for recreational waters. The organism has a multi-stage life cycle consisting of a motile feeding trophozoite stage, a non-replicating flagellate stage and an environmentally resistant cyst stage.
N. fowleri can be found worldwide in fresh water and soil. The organism has been isolated from both natural and artificial water supplies, including lakes, rivers, hot springs, swimming pools, hydrotherapy baths and tap water. No human or animal reservoirs have been identified. The organism prefers warmer waters and can tolerate temperatures of 40-45°C (Percival et al., 2004). Tropical and subtropical fresh waters and hot springs are particularly well suited for the survival of N. fowleri. In colder waters, it is thought that the cyst form may survive in river and lake sediments (Pond, 2005).
N. fowleri causes a disease of the central nervous system called primary amoebic meningitis (PAM), which is almost always fatal. Human infection occurs when water containing the amoeba is forcefully inhaled or splashed into the nasal passages (e.g., during diving, jumping, falling or swimming underwater). Following inhalation, the organism travels through the nasal passages to the brain, causing damage to the cells of the olfactory system and cerebral cortex. The onset of illness is rapid. Symptoms include severe headache, high fever, intracranial pressure, stiff neck, altered mental status and coma, ultimately leading to death. Treatment is possible but requires prompt diagnosis and aggressive antimicrobial therapy. The organism is reported to exhibit sensitivity to amphotericin B.
Naegleria have also been proposed as natural hosts for the bacterial pathogen Legionella. Harbouring within Naegleria is thought to provide Legionella with an environment suitable for replication, in addition to providing protection from environmental stresses.
Cases of PAM are extremely rare; it is estimated that in the United States, one case occurs for approximately every 2.5 million swimmers (Visvesvara and Moura, 2006). Surveillance data indicated that 29 cases of the disease were reported in the United States over the period 1992-2002, with an average occurrence of 0-6 cases per year (Moore et al., 1993; Kramer et al., 1996; Levy et al., 1998; Barwick et al., 2000; Lee et al., 2002; Yoder et al., 2004). Reported outbreaks have been limited to the southern United States, including Florida, Texas, Oklahoma, California, Georgia and North Carolina. To date, there have been no recorded cases of PAM as a result of recreational water contact in Canadian waters. The bulk of the evidence suggests that amoebic meningoencephalitis is an unlikely health concern in Canada. However, researchers have suggested that increasing lake temperatures brought on by climate change could result in an expanded prevalence of this organism (Rose et al., 2001; Schuster and Visvesvara, 2004). Thus the potential exists for this organism and disease to become an emerging concern for recreational waters in the northern United States and Canada in the future.
Acanthamoeba are small, free-living amoebae. The organisms possess a two-stage life cycle consisting of a trophozoite feeding stage and an environmentally resistant cyst stage. The genus Acanthamoeba contains approximately 20 species. A. culbertsoni, A. polyphaga and A. castellanii are the species most commonly associated with human infections.
Acanthamoeba are considered ubiquitous in the environment. They can be found in fresh, estuarine and marine waters, hot springs, soils and sewage, and human-made water supplies, such as tap water and air conditioning condensers.
Pathogenic species of Acanthamoeba are responsible for two distinct clinical illnesses: amoebic keratitis (AK), a painful, vision-threatening disease of the cornea caused by A. polyphaga and A. castellanii; and granulomatous amoebic encephalitis (GAE), a fatal disease of the central nervous system caused by A. culbertsoni. Infections occur via inhalation or through direct contact with the mucous membranes of the eye or through abraded or traumatized skin.
Although pathogenic Acanthamoeba species can have a waterborne transmission, recreational water contact is not considered to be a significant risk factor for either of these illnesses. The principal risk for AK is poor hygienic practices in contact lens wearers (use of contaminated solutions, inadequate disinfection practices). Infection can be acquired by wearing contact lenses while swimming in lakes or ponds; however, the risk is considered extremely low. Currently, recreational water contact is not considered a route for acquiring GAE.
Acanthamoeba have also been proposed as natural hosts for certain free-living bacterial pathogens, namely Legionella and Mycobacterium. Survival within Acanthamoeba is thought to provide these organisms with an environment suitable for replication, as well as to provide protection from environmental stresses.
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