partially cooked eggs in restaurants provide one example to illustrate this point (33). Through molecular epidemiologic techniques, a recent outbreak of Sa. enteritidis was traced to a single egg-producing farm that housed >400,000 egg-laying hens in five henhouses (a veritable poultry city!) (34, 35).

Infections due to Sa. enteritidis have been increasing throughout Europe and the United States so rapidly that by 1990, Sa. enteritidis surpassed the venerable Salmonella typhimurium as the most commonly isolated serotype from humans in the United States (36, 37). With 80,000 hens per henhouse, often with cages stacked one upon another, commercial egg-producing farms create a permissive environment for the rapid transmission of enteric pathogens such as Salmonella and Campylobacter jejuni among animals, thereby creating a reservoir of infection for humans.

Part of the appeal of fast-food chains is the consumer's expectation that the food prepared in all outlets will conform to uniform procedures, using comparable ingredients (often from the same source). Thus, a high level of consistency is demanded and expected by the consumers from each fast-food chain, irrespective of the state or country in which a particular outlet is found. This integral part of the appeal of fast food also makes it capable of disseminating infection widely through a common vehicle. Recent outbreaks of hemorrhagic colitis and hemolytic uremic syndrome due to enterohemorrhagic E. coli of serotype O157:H7 provide an excellent example (3842).

Enterohemorrhagic E. coli first came to be recognized in the U.S. as an enteric pathogen in 1982 when a multistate outbreak of an unusual clinical syndrome was seen in several midwestern and western states associated with the consumption of undercooked hamburgers (38). The clinical syndrome observed, hemorrhagic colitis, consisted of watery bloody diarrhea, without fever or fecal leukocytes (38). An unusual serotype of E. coli, O157:H7, was isolated from cases that had not previously been incriminated as a cause of diarrheal illness. Examination of the O157:H7 organism by various investigators revealed that this pathogen had amassed a fascinating array of virulence properties, including elaboration of phage-encoded potent Shiga-like toxins (43), a 60-MDa virulence plasmid associated with expression of novel fimbriae (44), and a chromosomal gene (45) that induces attaching and effacing lesions of intestinal mucosa (46). It was subsequently shown that serotype O157:H7 is a prototype within a new category of diarrheagenic E. coli, referred to as enterohemorrhagic E. coli; multiple other O:H serotypes also fall within this category, most notably O26:H11 and O111:NM (42), among others.

It rapidly came to be recognized that ≈1–2% of individuals with



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