|
Article Excerpt
The Walkerton, Canada, waterborne outbreak of 2000 resulted from entry of Escherichia cell O157:H7 and Campylobacter spp. from neighboring farms into the town water supply. Isolates of Campylobacter jejuni and Campylobacter coil obtained from outbreak investigations were characterized by phenotypic and genotypic methods, including heat-stable and heat-labile serotyping, phage typing, biotyping, fla-restriction fragment length polymorphism (RFLP) typing, and pulsed-field gel electrophoresis. Two main outbreak strains were identified on the basis of heat-stable serotyping and fla-RFLP typing. These strains produced a limited number of types when tested by other methods. Isolates with types indistinguishable from, or similar to, the outbreak types were found only on one farm near the town of Walkerton, whereas cattle from other farms carried a variety of Campylobacter strains with different type characteristics. Results of these analyses confirmed results from epidemiologic studies and the utility of using several different typing and subtyping methods for completely characterizing bacterial populations.
**********
An outbreak of Campylobacter jejuni in a farming community in southern Ontario, Canada, in 1985 resulted from contamination of well water caused by spring run-off and heavy rains (1). In May 2000, a second waterborne outbreak of Escherichia coli O157:H7 and Campylobacter occurred in Bruce County, Ontario. Well water serving the town of Walkerton was contaminated by surface water carrying livestock waste immediately after heavy rains (2,3). A detailed microbiologic and epidemiologic analysis of the most recent outbreak may provide insights that could help make this type of outbreak less frequent.
Most sporadic cases of campylobacteriosis are associated with preparation or consumption of poultry products (4). Outbreaks have been associated with consumption of unpasteurized milk or unchlorinated water (5). An estimated 20% of cases of illness caused by C. jejuni are due to vehicles of infection other than food, including water (6). Waterborne outbreaks of Campylobacter tend to occur in spring or early fall, an association attributed to seasonality of surface water contamination and infection in cattle herds (5). Contaminated water sources have been implicated in outbreaks involving E. coli O157:H7 and Campylobacter together in Scotland (7) and in New York State (8,9). The former outbreak resulted from sewage contamination of the water supply of a small village in Fife, Scotland. The latter outbreak was associated with contamination of wells at a state fair (10). Excrement from birds and animals, including cattle, has been shown to contaminate surface water supplies used by humans infected with Campylobacter (9).
Campylobacter spp. have been found to cause waterborne outbreaks worldwide; such outbreaks are a particular problem in Scandinavian countries where many people drink untreated water from streams and other sources (11). Untreated surface water has also been implicated in Campylobacter outbreaks in New Zealand (12,13), Finland (14), England, Wales (15,16), Australia (17), and the United States (18). In Canada, outbreaks have been rarely detected and have been associated with contamination of surface water (19,20) and consumption of unpasteurized milk (21).
In the United States, disease caused by C. jejuni or C. coli has been estimated to affect 7 million people annually, causing 110-511 deaths and costing $1.2-$6 billion (22). These organisms are responsible for 17% of all hospitalizations related to foodborne illness in the United States, and although associated with a much lower case-fatality rate than Salmonella spp. and E. coli O157:H7, they account for 5% of food-related deaths (6). Although the incidence of Campylobacter infections generally appears to be higher in industrialized than in developing nations, some evidence exists that campylobacteriosis may be important from a social and economic point of view (23).
Epidemiologic and microbiologic analyses were undertaken to better understand the circumstances leading to the Walkerton outbreak. C. jejuni was isolated from patients associated with the outbreak, and C. jejuni and C. coli were isolated from animals and animal manure on farms located near the town wells. This work summarizes the phenotypic and genotypic typing results for isolates associated with the outbreak.
Materials and Methods
Epidemiologic Investigations
Identification of the outbreak, definition of cases, and the results of epidemiologic descriptive and cross-sectional studies have been described (2,3). Isolates from persons who did not meet all requirements for the case definition, but who resided in southwestern Ontario and became ill during the period of the outbreak, were also sent to the National Laboratory for Enteric Pathogens (NLEP), Winnipeg, Manitoba, for further analysis. A detailed description of the epidemiologic investigations is in preparation.
Environmental Specimens
Environmental studies related to the outbreak have been described previously (2,3). Initial investigations identified 13 livestock farms within a 4-km radius of the three wells serving the town of Walkerton. From May 30 to June 13, 2000, a minimum of five manure samples per farm were obtained and tested for human enteric pathogens. Bovine rectal swabs and manure were collected from a subset of these farms in follow-up studies on June 13. All specimens were screened for Campylobacter spp., and isolates were forwarded to NLEP for further testing.
Processing of Specimens
Patient stool specimens were collected into Cary-Blair transport medium and sent to the Central Public Health Laboratory, Ministry of Health and Long-Term Care, Toronto, Ontario. Specimens from animal manure were collected aseptically in sterile bags and forwarded to the same laboratory. Stools (approximately 1 g) from both sources were added into liquid enrichment medium (LEM) or directly onto charcoal-selective medium (CSM) and incubated at 42[degrees]C in a microaerobic atmosphere (5% [O.sub.2], 10% C[O.sub.2], 85% [N.sub.2]) for 24 h and 48 h. Cultures in LEM were subcultured to CSM and incubated as indicated above. Isolates submitted to the NLEP were routinely cultured on Mueller-Hinton agar (Oxoid Ltd., London, England) containing 10% sheep blood and stored frozen at -70[degrees]C in glycerol peptone water. Isolates were routinely incubated at either 37[degrees]C or 42[degrees]C in a microaerobic atmosphere.
Identification of Isolates
Colonies suspected of being Campylobacter were Gram stained and tested for oxidase, catalase, and hippurate hydrolysis. Presumptive identification of C. coli was achieved by the indoxyl acetate test and by determining susceptibility to nalidixic acid (30-[micro]g disk) and cephalothin (30-[micro]g disk). Biotyping was performed as described by Lior (24). In addition to biotyping, the polymerase chain reaction-restriction fragment length polymorphism (PCRRFLP) identification scheme described by Marshall et al. (25) was used to confirm species identification. Primers specific to C. jejuni (25) and to C. coli (26) were used to confirm the identity of any "hippurate-negative" C. jejuni. Any isolates that were hippurate-negative in the tube test but positive by PCR for the hippuricase gene and negative by...
|
