AN OUTBREAK OF ESCHERICHIA-COLI O157-H7 INFECTIONS ASSOCIATED WITH LEAF LETTUCE CONSUMPTION

In July 1995, 40 Montana residents were identified with laboratory-con firmed Escherichia coli O157:H7 infection; 52 residents had bloody dia rrhea without laboratory confirmation. The median age of those with la boratory-confirmed cases was 42 years (range, 4-86); 58% were female. Thirteen patients were hospitalized, and 1 developed hemolytic-uremic syndrome. A case-control study showed that 19 (70%) of 27 patients but only 8 (17%) of 46 controls reported eating purchased (not home-grown ) leaf lettuce before illness (matched odds ratio, 25.3; 95% confidenc e interval, 3.9-1065.6). Pulsed-field gel electrophoresis identified a common strain among 22 of 23 isolates tested. Implicated lettuce was traced to two sources: a local Montana farm and six farms in Washingto n State that shipped under the same label. This outbreak highlights th e increasing importance of fresh produce as a vehicle in foodborne ill ness. Sanitary growing and handling procedures are necessary to preven t these infections.