Enterohemorrhagic Escherichia coli O157 (EHEC) causes severe complications such as hemolytic uremic syndrome. Contaminated ready-to-eat (RTE) food is one of the vehicles of multijurisdictional outbreaks of foodborne disease worldwide. Multijurisdictional (covering cities, towns, and villages) outbreaks of EHEC are usually linked to an increase in cases, and here we describe such an outbreak involving 29 cases in October 2017 in the Niigata Prefecture. After prefecture-wide active case finding, we conducted a case-control study of 29 cases with eligible data who tested positive for EHEC. To determine the association of the outbreak with risk factors, we compared these cases with 38 controls selected from family and acquaintances who were both symptom free and tested negative for EHEC. The largest number of cases was in the 20-29-year age group (7/29; 24%) and most were women (20/29; 69%). All 29 cases had an identical or similar multilocus variable number tandem-repeat analysis (MLVA) profile. Of these, 76% (22/29) had consumed some type of grilled skewered meat. Also, 69% (20/29) had consumed grilled skewered meat produced by company X. EHEC infection was strongly associated with the consumption of grilled skewered meat produced by any food processing company (odds ratio [OR] = 11.8, confidence interval [95% CI]: 3.7-37.4) and by company X (OR = 9.8, 95% CI: 3.2-30.7). At company X, the skewered meat was grilled to 95°C and then removed from the grilling area to meat trays. The meat trays were not sufficiently washed and disinfected. Testing indicated that the facility was negative for EHEC but four asymptomatic employees tested positive for EHEC. Company X was temporarily closed and voluntarily recalled the foods. We recommend that all employees sufficiently wash and disinfect meat trays to prevent contamination of RTE food, avoid cross-contamination of grilled skewered meat through the environment by regularly cleaning the facility, and appropriately practice self-health care.
Keywords: enterohemorrhagic Escherichia coli O157; food processing facility; multijurisdictional outbreak; multilocus variable number tandem-repeat analysis; ready-to-eat food; sanitation.