A Multistate Outbreak of Escherichia coli O157:H7—Associated Bloody Diarrhea and Hemolytic Uremic Syndrome From Hamburgers

Abstract

Objective. —To determine the source of and describe a large outbreak ofEscherichia coliO157:H7 infections in Washington State. Design. —Case-control study; environmental investigation; provider-based surveillance forE coliO157:H7 infections. Setting. —Chain of fast-food restaurants, hospitals, physician offices, local laboratories, and local health departments. Participants. —Patients with diarrhea and neighborhood controls. A case was defined as diarrhea with culture-confirmedE coliO157:H7 infection or postdiarrheal hemolytic uremic syndrome (HUS) occurring from December 1, 1992, through February 28, 1993, in a Washington State resident. Controls were age- and neighborhood-matched friends of the first 16 case patients. Interventions. —Announcement to the public; recall of implicated hamburger lots. Main Outcome Measure. —Abatement of outbreak due toE coliO157:H7. Results. —Infection was associated with eating at a fast-food chain (chain A) in the 10 days before symptoms began. Twelve (75%) of 16 case patients but no controls had eaten at chain A (matched odds ratio undefined; lower 95% confidence interval, 3.5;P<.001). In total, 501 cases were reported, including 151 hospitalizations (31%), 45 cases of HUS (9%), and three deaths. Forty-eight patients (10%) had secondary infections. Of the remaining 453 patients (90%), 398 (86%) reported eating at a Washington chain A restaurant; 92% of them reported eating a regular hamburger. The pulsed-field gel electrophoresis pattern of theE coliO157:H7 strains isolated from all regular hamburger lots of a single production date shipped to Washington was identical to that of the strains isolated from patients. Ten (63%) of 16 regular hamburgers cooked according to chain A policy had internal temperatures below 60°C. Public health action removed more than 250 000 potentially contaminated hamburgers, preventing an estimated 800 cases. Conclusions. —ThisE coliO157:H7 outbreak, the largest reported, resulted from errors in meat processing and cooking. Public health surveillance through state-mandated reporting ofE coliO157:H7 infection as is carried out in Washington State was critical for prompt outbreak recognition and control. Measures should be developed to reduce meat contamination. Consumers and food service workers should be educated about cooking hamburger meat thoroughly. (JAMA. 1994;272:1349-1353)