FIGURE 1-1 Risk-assessment structure for E. coli O157:H7 in ground beef. (Reproduced from USDA-FSIS (2001) Figure 1-1.)

This chapter summarizes the content of the FSIS risk assessment as presented in the draft report and is intended as a reference for readers who do not have ready access to that document.² The draft risk assessment itself is reviewed in the next five chapters and the modeling approach and implementation in Chapter 7.

The model is divided into three exposure assessment modules (Production, Slaughter, and Preparation), a Hazard Characterization Module (also known as dose-response assessment), and a Risk Characterization Module, which estimates the risk of illness from E. coli O157:H7 in ground beef. Figure 1-1 is a graphic representation of those components, which are discussed below.

The Production Module estimates the prevalence of E. coli O157:H7 in live cattle entering US slaughter plants. Prevalence, in this context, is the proportion of a population that is infected. In the model, cattle are divided into two groups: breeding cattle (mature cattle bred to produce milk and calves) and feedlot cattle (steers and heifers specifically intended for slaughter). The distinction is made because breeding and feedlot cattle differ in their slaughter and in the processing and distribution of their meat, and because some evidence suggests that E. coli prevalence varies between the two groups of cattle. About 20% of all cattle slaughtered in the United States are breeding cattle; the remaining 80% are feedlot cattle. Some 15% of beef consumed in the United States is imported from other countries; the model assumes that any E. coli O157:H7 contamination in imported beef would be equivalent to that in domestic beef.