Background . In August and November 2004, 2 clusters of diarrhea cases occurred among patrons of 2 affiliated sushi restaurants (sushi restaurant A and sushi restaurant B) in Nevada. In August 2004, a stool sample from 1 ill sushi restaurant A patron yielded enterotoxigenic Escherichia coli (ETEC). In December 2004, we investigated a third cluster of diarrhea cases among sushi restaurant B patrons.

Methods . We defined a case as diarrhea in a person who ate at sushi restaurant B from 3 December through 13 December 2004. Control subjects were individuals who dined with case patients but did not become ill. Duplex polymerase chain reaction was used to detect genes coding for heat-stable and heat-labile enterotoxins of ETEC.

Results . One-hundred thirty patrons of sushi restaurant B reported illness; we enrolled 36 case patients and 29 control subjects. The diarrhea-to-vomiting prevalence ratio among patients was 4.5. Illness was associated with consumption of butterfly shrimp (estimated odds ratio, 7.2; 95% confidence interval, 1.1 to infinity). The implicated food was distributed to many restaurants, but only sushi restaurant B patrons reported diarrhea. We observed poor food-handling and hand hygiene practices at sushi restaurant B. Stool samples from 6 of 7 ill patrons and 2 of 27 employees who denied illness yielded ETEC.

Conclusions . ETEC was identified as the etiologic agent of a large foodborne outbreak at a sushi restaurant in Nevada. Poor food-handling practices and infected foodhandlers likely contributed to this outbreak. Although ETEC is a well-documented cause of domestic foodborne outbreaks, few laboratories can test for it. Earlier recognition of ETEC infections may prevent subsequent outbreaks from occurring.