O157:H7-tainted raw ground beef are likely to be important sources of human illness (Buchanan and Doyle, 1997).
A case-control analysis of sporadic infection with E. coli O157:H7 by Mead et al. (1997) substantiates that notion. It determined that most ill persons in question had eaten hamburgers prepared at home and that the primary risk factors associated with infection were food preparers who had not washed their hands or work surfaces after handling raw ground beef. The investigators concluded that in many instances hamburgers were not the direct vehicle of transmission of E. coli O157:H7, but rather that transmission occurred more commonly when the food preparers’ hands, contaminated by raw ground beef, were allowed to cross-contaminate other meal items or utensils. In a multistate outbreak of E. coli O157:H7 infection in 1995, cross contamination from raw ground beef was identified as the likely contributing factor associated with eating cooked ground-beef sandwiches prepared at fast-food restaurants of a specific chain (CDC, 1996).
Although they did not address the issue of E. coli O157:H7 directly, two studies released while the draft risk assessment was under development support the notion that cross contamination during food preparation is an important risk factor for foodborne illness in general. Audits International (2001) published a study of food-preparation practices that identified cross contamination (25% of failures) as the third most-common critical violation1 of good hygienic practices in the home. Previous Audits International studies had ranked it as the most common critical violation, with a frequency of 71% in 1997 and 31% in 1999. Another study researching commercial and institutional food operations was prepared by the Food and Drug Administration (FDA, 2000). Researchers at FDA found that 15% of fast-food restaurants and 44% of full-service restaurants examined were out of compliance with one or more items in the category “contaminated equipment/protection from contamination”. Those items included whether raw animal foods were separated from one another, whether raw and ready-to-eat foods were separated, and whether surfaces and utensils were cleaned or sanitized.
The Food Safety and Inspection Service (FSIS) of the US Department of Agriculture (USDA) itself identifies cross contamination during preparation as a significant factor in food safety. Two of the four steps in USDA’s Fight BAC!2 campaign—”Clean—wash hands and surfaces often” and “Separate—don’t cross-contaminate”—address interventions intended to minimize it.