Enterotoxigenic Escherichia coli (ETEC) is an emerging cause of foodborne outbreaks of infection in the United States, yet its epidemiology is not completely understood. In September 2004, we investigated an outbreak of infection due to ETEC at an Illinois corporation following a meal served to approximately 700 employees. Clinical samples were negative for enteric pathogens and were tested for ETEC using stool culture and polymerase chain reaction (PCR). An environmental investigation was conducted to determine whether food-service practices or conditions led to this outbreak. A case of illness caused by ETEC was defined as onset of diarrhea and > or =1 of the following symptoms during 23-30 September 2004: cramps, vomiting, nausea, headache, or weight loss. The 111 ill employees interviewed had only 1 meal in common. Cucumber salad and noodle salad from that meal were associated with illness; no food was available for testing. A PCR test for ETEC in stool was positive in samples from 6 of 11 patients; 3 ETEC serotypes were detected. The environmental investigation revealed no critical violations. The median duration of diarrhea (7 days) was longer than that observed for the majority of outbreaks of ETEC infection (4 days) and was associated with consumption of carbonated beverages (odds ratio, 4.5; 95% confidence interval, 2.0-10.3). Emerging features of ETEC identified in this outbreak include the organism's role in domestic outbreaks and its ability to cause prolonged diarrheal illness. Additionally, integrating the results of nonculture-based diagnostic techniques into foodborne outbreak surveillance presents challenges under the current guidelines of the Centers for Disease Control and Prevention.
