Escherichia coli O157:H7 remains a public health problem in the United States despite a dramatic increase in the awareness of, and concern about, foodborne infections since the 1993 multistate E. coli O157:H7 epidemic. Although surveillance data can be difficult to interpret, the incidence of endemic disease caused by this organism is probably not increasing, and might be decreasing, at least in selected populations. With increased recognition of E. coli O157:H7 infection has come the investigation of increasing number of outbreaks, leading to the recognition of many “new” vehicles, including some foods not traditionally associated with enteric infections, such as dry-cured salami and lettuce. Molecular fingerprinting techniques are being used to track the transmission of E. coli O157:H7 through human populations. Analysis of DNA encoding virulence factors and surface antigens suggests that diarrheagenic E. coli have evolved by acquiring large DNA fragments, with subsequent chromosomal recombination. Some Shiga toxin–producing E. coli other than E. coli O157:H7 are no doubt pathogens, but the majority of these toxigenic strains found in food are probably not virulent. More research is needed to define the characteristics that render selected Shiga toxin–producing organisms harmful to humans.
† Presented as part of an ILSI-sponsored symposium, Global Perspectives on Escherichia coli O157:H7 and Other Serotypes, at the 83rd IAMFES Annual Meeting in Seattle, Washington 30 June to 3 July 1996.