in expression. We present below a number of specific suggestions regarding defined and undefined terms.
“Typical” individual risk is the term applied to the risk posed for someone who purchases ground beef that is contaminated with E. coli O157:H7 organisms at the median concentration, who stores and cooks that product in a way that is consistent with the median growth and cooking distributions, and who consumes a single serving. Because the definition does not describe a “typical” exposure, the committee suggests that that word be changed, perhaps to hypothetical or illustrative.
Duration of exposure is defined in the draft as “the length of time (e.g., per serving, per annum, or lifetime) for which a risk estimate was assessed.” The definition is confusing. Relating a serving to a duration of exposure is awkward. The committee suggests that this term, which is used only twice in text, be dropped.
The term dose is defined as the number of E. coli O157:H7 in a single serving of ground beef. That is consistent with the draft Food and Drug Administration (FDA)-USDA Listeria risk assessment (2001). However, in chemical risk assessments, dose is usually defined as grams per kilogram of body weight of a subject. The committee suggests that the report’s definition of dose draw attention to the different meaning of this term in microbial risk assessments.
The draft cites sensitivity analysis as “the quantitative process of identifying factors (model inputs) in the farm-to-table continuum that contribute to the occurrence of E. coli O157:H7 in ground beef or the subsequent risk of illness” (p. 130). That definition is tangentially related to the more traditional understanding of the term: the quantification of the effects of changes in model inputs on model outputs. However, it fails to capture the sense in which most risk analysts apply it: the systematic investigation of whether and to what extent changes in model inputs across a plausible range of values affect model outputs. The committee suggests that the final risk assessment adopt the more common definition of sensitivity analysis. The related terms correlation analysis and dependency analysis should also be more clearly and completely documented on the basis of established definitions.
The “risk of illness” is addressed throughout the chapter, but no formal definition of the conditions covered by illness is provided. As the draft notes (pp. 22–23), ingestion of E. coli O157:H7 can result in a wide array of outcomes, including asymptomatic infection, abdominal cramps, nonbloody diarrhea, hemorrhagic colitis, hemolytic uremic syndrome (HUS), and thrombotic thrombocytopenic purpura (TTP). The chapter needs a clear definition, and, depending on the conditions covered, risk of infection may be a more appropriate term. Furthermore, “annual risk” and “risk per serving” are both referred to as risk of illness in the chapter. The