Genotypic characterization and prevalence of virulence factors among Canadian Escherichia coli O157:H7 strains.

In this study, the association between genotypic and selected phenotypic characteristics was examined in a collection of Canadian Escherichia coli O157:H7 strains isolated from humans and cattle in the provinces of Alberta, Ontario, Saskatchewan, and Quebec. In a subset of 69 strains selected on the basis of specific phage types (PTs), a strong correlation between the lineage-specific polymorphism assay (LSPA6) genotype and PT was observed with all strains of PTs 4, 14, 21, 31, 33, and 87 belonging to the LSPA6 lineage I (LSPA6-LI) genotype, while those of PTs 23, 45, 67, and 74 belonged to LSPA6 lineage II (LSPA6-LII) genotypes. This correlation was maintained when additional strains of each PT were tested. E. coli O157:H7 strains with the LSPA6-LI genotype were much more common in the collection than were the LSPA6-LII or lineage I/II (LSPA6-LI/II)-related genotypes (82.6, 11.2, and 5.8%, respectively). Of the strains tested, proportionately more LSPA6-LI than LSPA6-LII genotype strains were isolated from humans (52.7% versus 19.7%) than from cattle (47.8% versus 80.2%). In addition, 96.7% of the LSPA6-LII strains carried the stx(2c) variant gene, while only 50.0% of LSPA6-LI/II and 2.7% of LSPA6-LI strains carried this gene. LSPA6-LII strains were also significantly more likely to possess the colicin D gene, cda (50.8% versus 23.2%), and have combined resistance to streptomycin, sulfisoxazole, and tetracycline (72.1% versus 0.9%) than were LSPA6-LI strains. The LSPA6 genotype- and PT-related characteristics identified may be important markers of specific ecotypes of E. coli O157:H7 that have unique epidemiological and virulence characteristics.

Use of the oxford multilocus sequence typing protocol and sequencing of the flagellin short variable region to characterize isolates from a large outbreak of waterborne Campylobacter sp. strains in Walkerton, Ontario, Canada.

The Walkerton (Ontario, Canada) outbreak of waterborne Escherichia coli O157:H7 and Campylobacter jejuni was quite limited in both space and time, making it a good model for exploring the utility of different typing and subtyping methods for the characterization of relationships among isolates of these organisms. We have extended previous work with these organisms through analysis by the Oxford multilocus sequence typing (MLST) and the flagellin short variable region (fla-SVR) sequencing methods. Additional isolates not epidemiologically related to the Walkerton outbreak have also been included. Both sequencing methods identified and differentiated between Walkerton outbreak strains 1 and 2. When these strains were compared with isolates that were not part of the outbreak, the information produced by the fla-SVR method more often correlated with epidemiological findings than that produced by MLST, though both methods were required for optimal discrimination. The MLST data were more relevant in terms of the overall population structure of the organisms. Both mutation and recombination appeared to be responsible for generating diversity among the isolates tested.

Increased burden of illness associated with antimicrobial-resistant Salmonella enterica serotype typhimurium infections.

This study investigated the burden of illness associated with 440 cases of Salmonella enterica serotype Typhimurium infection identified in Canada between December 1999 and November 2000. We categorized case subjects' infections by definitive phage type 104 (DT104) and antimicrobial-resistance patterns. These variables were then investigated as risk factors for hospitalization. Hospitalization was more likely to occur among case subjects whose infections were resistant to at least ampicillin, chloramphenicol and/or kanamycin, streptomycin, sulphamethoxazole, and tetracycline (R-type AK/CSSuT; odds ratio [OR], 2.3; P=.003), compared with case subjects with AK/CSSuT-susceptible infections, and among case subjects with non-DT104 R-type AKSSuT infections (OR, 3.6; P=.005), compared with case subjects with non-DT104 AKSSuT-susceptible infections. In contrast, hospitalization rates did not differ between case subjects with DT104 infections and case subjects with non-DT104 infections or between case subjects with DT104 R-type ACSSuT infections and case subjects with DT104 ACSSuT-susceptible infections. We estimated that 57% of the hospitalizations among AK/CSSuT case subjects and 72% of the hospitalizations among non-DT104 AKSSuT case subjects were attributable to the resistance patterns of the infections.

A descriptive study of human Salmonella serotype typhimurium infections reported in Ontario from 1990 to 1998.

BACKGROUND: Salmonella infections cause gastrointestinal and systemic diseases worldwide and are the leading causes of food-borne illnesses in North America (1-4). Salmonella serotype typhimurium (ST), in particular, is increasingly becoming a major public health concern because of its ability to acquire multiple resistant genes (5,6). OBJECTIVE: To describe demographic, temporal and geographical distributions, and reported risk factors of nonoutbreak cases of ST reported to a surveillance system in Ontario. METHODOLOGY: Descriptive analyses were performed on data on salmonellosis cases reported in Ontario between 1990 and 1998. Direct age- and sex-standardized rates were computed, and temporal trend analyses were performed using simple linear regression and a general additive model with a locally weighted regression (LOESS) smoother. RESULTS: The mean annual rates of infections with all Salmonella serotypes and with ST were 27 cases per 100,000 persons and 3.7 cases per 100,000 persons, respectively. Males and children under five years of age had significantly higher rates of both ST and ST definitive type 104 (DT104) infections. There was also evidence of temporal clustering of all strains of Salmonella, with significantly more cases being reported during the summer. Significantly higher rates of ST DT104 were observed in urban areas compared with rural areas, suggesting potential differences in the geographical distribution of risk factors. CONCLUSIONS: Information on demographic, temporal and geographical distributions, and risk factors is critical in planning disease control strategies. Further prospective analytical observation studies are needed to gain a better understanding of the epidemiology of ST and ST DT104 in Ontario, which will better guide disease control decisions.

Outbreak of Escherichia coli 0157:H7 related to animal contact at a petting zoo.

OBJECTIVE: To determine the cause of an outbreak of Escherichia coli 0157:H7 related to animal exposures so that further transmission could be prevented. DESIGN: Description of laboratory investigations and a case control study. SETTING: Agricultural pavilion at an annual fair in Ontario. POPULATION: People with laboratory evidence of E coli 0157:H7 (seven people) and others with diarrhea (155 people) who called the health unit following a media release were interviewed. Animals that were accessed most frequently by the public in the agriculture pavilion were tested for E coli 0157:H7. In the case control study, a case was defined as someone with laboratory confirmed E coli 0157:H7, or someone who developed severe or bloody diarrhea two to eight days after attending the agricultural pavilion at the fair (61 people). A convenience sample of people who attended the agricultural pavilion but did not develop diarrhea was selected as the control group (89 people). INTERVENTIONS: Human and animal E coli 0157:H7 specimens were subtyped. Cases and controls were interviewed using a standardized questionnaire. RESULTS: Subtyping of the seven human isolates of E coli 0157:H7 revealed five that were of an extremely uncommon phage type. Three samples from goats and one from sheep at the petting zoo in the agricultural pavilion were of this same phage type. The case control study also implicated goats (odds ratio [OR] 3.65; 95% CI 1.63 to 8.52) and sheep (OR 2.94; 95% CI 1.33 to 6.57) from the petting zoo. CONCLUSIONS: Results of this investigation suggest strongly that the goats and sheep from the petting zoo were the source of this outbreak of E coli 0157:H7.