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BACKGROUND: Escherichia coli O157:H7 is a top cause of foodborne-related hospitalization in the United States, with ~73,000 illnesses and 61 deaths annually. In July, Mraicopa County Department of Public Health (MCDPH) was notified of bloody diarrhea in 3 hospitalized patients who reported eating at Restaurant A. We sought to identify cases, and sources, to prevent additional illnesses.
METHODS: Probable cases had diarrhea or hemolytic uremic syndrome (HUS) within 10 days of Restaurant A patronage during July 18–30; confirmed cases had matching pulsed-field gel electrophoresis patterns. MCDPH conducted a case-control study; subjects were identified by using press releases to encourage ill persons to contact public health, notifying hospitals, and calling Restaurant A patrons identified from receipts. Controls ate at Restaurant A and had no subsequent illness. Bivariate and logistic regression analysis were conducted on data collected from questionnaires. Environmental investigation included restaurant inspection, food ingredient traceback, and laboratory analysis.
RESULTS: MCDPH identified 94 (including 11 confirmed) cases in patients aged 2–88 (median 32) years; 53 (56.4%) were female. Thirty-three (35.1%) persons sought medical care, including 2 (2%) with HUS. None died. In a logistic regression model of ingredients with significant bivariate associations, only lettuce remained significant (Odds Ratio 3.2, 95% confidence interval 1.5–6.8). Lettuce was consumed by 72.8% (59/81) of cases and 42.4% (42/99) of controls. No pathogenic E. coli were identified in environmental samples but total coliforms >1400 were isolated from lettuce on two separate occassions. Traceback revealed the lettuce distributer supplied other restaurants without reported illnesses. Restaurant A reported no employee illnesses.
CONCLUSIONS: An E. coli O157:H7 outbreak was traced to one restaurant; data indicate that contaminated lettuce was associated with illness. Identifying more effective methods to prevent contamination of uncooked foods is warranted.