EnterohemorrhagicEscherichia coliin the United States

Escherichia coli O157:H7, the documented cause of over 100 outbreaks of human disease in the United States since it emerged as an epidemic cause of foodborne illness in 1982, is a textbook illustration of today's emerging microbial pathogen. Its ‘emergence’ apparently is associated with genetic changes in the organism, changes in food production and distribution, human behavior, and changes in disease reporting requirements that brought increased recognition. The largest documented outbreak in the United States, with over 700 illnesses and four deaths, occurred in 1993 in the western United States. The vehicle of transmission was the same as in 1982 — contaminated hamburger, quickly and widely distributed through ‘fast food’ restaurant chains. This paper will examine each of these contributing factors, trace the emergence of E. coli O157:H7 in the United States, discuss methods for identifying vehicles of epidemic and sporadic transmission, and control measures that are being taken. E. coli typically are benign inhabitants of the human and animal gut, and are so ubiquitous that their detection is used to monitor fecal contamination and sewage treatment effectiveness. But not all E. coli are benign. Several dozen have been recognized as human pathogens and are associated with at least five different pathogenic mechanisms. Some, like the classic enteropathogenic E. coli (EPEC) strains, have enteroadhesive genes ( eae ) on their chromosomes that are essential for the production of the characteristic attaching and effacing lesions. Enterotoxigenic (ETEC) strains produce toxins and enteroinvasive strains possess invasive qualities [1]. Molecular genetic studies indicate that E. coli O157:H7 evolved from an EPEC progenitor that acquired the Shiga-toxin gene ( stx ) [2]. Having this gene and expressing the toxins, classifies E. coli O157:H7 as a member of the Shiga-toxin producing E. coli (STEC). The gene is essentially indistinguishable from that on the chromosome of Shigella dysenteriae …