Escherichia coli O157:H7 in Ground Beef Review of a Draft Risk Assessment (2002) / Chapter Skim
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5 Hazard Characterization
5 Hazard Characterization
Pages 71-88
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From page 71... ...
, and the upper- and lower-bound dose-response curves based on surrogate pathogens; and · validating the derived dose-response function for E cold 0157:H7 by comparison with data from an outbreak associated with ground beef on which clinical, epidemiologic, and bacteriologic (isolation of pathogen from uncooked hamburger patties)
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From page 72... ...
cold other than 0157:H7 also possess these properties. The common virulence factors carried by EHEC include a chromosomal pathogenicity island that encodes proteins allowing the bacteria to cause attaching and effacing lesions of the intestinal mucosa, an approximately 60 megadalton plasmid that encodes attachment factors and an enterohemolyin, and bacteriophages that encode Shiga toxins 1, 2, or both.
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From page 73... ...
Because non-0157:H7 serotypes contribute to the EHEC disease burden particularly as a cause of HUS the committee suggests that the decision to exclude these serotypes be revisited. If the final risk assessment is limited to 0157:H7, the committee recommends that the decision and its implications for the model be explicitly discussed in the Hazard Characterization chapter.
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From page 74... ...
However, contaminated raw ground beef may be epidemiologically important and lead to clinical infections even if the meat that is ultimately ingested is properly cooked and harbors no living 0157:H7 or other EHEC organisms. The reason is that inadequate cooking, mistakes in food handling, or poor hygiene in the kitchen may lead to cross contamination of other food vehicles that may be eaten raw (salads, for example)
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From page 75... ...
Although Shigella may indeed be transmitted by contaminated food and water vehicles, and outbreaks due to contaminated food vehicles have been described, in fact the vast body of accumulated epidemiologic data indicates that Shigella are most often transmitted through direct person-to-person contact by means of fecally contaminated hands or fomites.~ Thus, transmission of Shigella correlates with the level of personal hygiene rather than sanitation or food hygiene. Populations that manifest compromised personal hygiene are at high risk of transmission of Shigella even in industrialized countries.
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From page 76... ...
, exhibit an unusual degree of acid resistance among bacterial enteropathogens. The fact that ground beef and some other common food vehicles responsible for transmission of EHEC 0157:H7 involve cooking means that the ingested inocula, like those of Shigella, can be quite small.
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From page 77... ...
· When fasting healthy adult US volunteers ingested 106 CFU of V cholerae 01 with NaHCO3 buffer (which neutralizes gastric acid)
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From page 78... ...
flexneri 2a were fed in 45 ml of skim milk to immunologically naive healthy adult community volunteers; the overall clinical attack rate was 48% (24 of 50) , with a range of 33% to 58% for attack rates in individual challenge studies.
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From page 80... ...
Extrapolation of Dose-Response Data to High-Risk Age Groups Whatever dose-response data (from studies with Shigella or other bacterial enteropathogens) are used as surrogates to help to estimate the doseresponse relationship for 0157:H7 and other EHEC, it must be remembered that the data are derived from experimental challenge studies in healthy adults.
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From page 81... ...
Role of Host Factors in Clinical Response to Challenge with Bacterial Enteropathogens 81 It is obvious in experimental challenge studies that different healthy adults may respond differently to ingestion of identical inocula of a bacterial enteropathogen. Prior immunity or nonspecific innate immune mechanisms can partly explain the differences.
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From page 83... ...
Severe Clinical Outcomes and Sensitive Populations The FSIS draft offers two observations regarding severe clinical outcomes and sensitive populations that the committee would like to highlight. It asserts that "estimating the clinical outcomes of symptomatic infection is essential for future cost-benefit analyses of intervention options" (p.
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From page 84... ...
In fact, epidemiologic and microbiologic data suggest that the true EHEC dose-response function is likely to resemble that of Shigella. The failure to account for non-0157:H7 as a cause of hemorrhagic colitis and HUS underestimates the overall burden of EHEC disease in the United States and the benefits that may derive from future interventions.
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From page 85... ...
1992. Enterohemorrhagic Escherichia cold associated with hemolytic-uremic syndrome in Chilean children.
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From page 86... ...
1992. Safety, immunogenicity, and efficacy in monkeys and humans of invasive Escherichia cold K-12 hybrid vaccine candidates expressing Shigella flexneri 2a somatic antigen.
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From page 87... ...
cold isolated from Chilean children with intestinal infections or hemolytic uremic syndrome]
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From page 88... ...
1999. Clonal diversity of Chilean isolates of enterohemorrhagic Escherichia cold from patients with hemolytic-uremic syndrome, asymptomatic subjects, animal reservoirs, and food products.
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