Epidemiological analysis of a large enterohaemorrhagic Escherichia coli O111 outbreak in Japan associated with haemolytic uraemic syndrome and acute encephalopathy

Abstract

A large outbreak of enterohaemorrhagic Escherichia coli (EHEC) O111 and O157 occurred in Japan in April 2011. We conducted an unmatched case-control study and trace-back investigation to determine the source of EHEC O111 infection and risk factors for severe complications. Pulsed-field gel electrophoresis was performed to help define cases. A total of 86 individuals met the case definition. Of these, 40% experienced haemolytic uraemic syndrome (HUS), 24% acute encephalopathy, and 6% died. Illness was significantly associated with eating the raw beef dish yukhoe (odds ratio 19·64, 95% confidence interval 7·03-54·83), the likely food vehicle. EHEC O111 and its closely related stx-negative variants were found in the beef. HUS occurred most frequently in individuals aged 5-9 years, and this age group was significantly associated with acute encephalopathy. The prevalence of HUS and acute encephalopathy was higher than in previous non-O157-related outbreaks, indicating a high risk of severe complications.