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.

Keywords: Escherichia coli infection; foodborne diseases; infectious disease outbreaks.

Fig. 1.

Flowchart of cases and controls in the outbreak investigation. ^a Suspected cases; ^b EHEC O157 isolated only; ^c tested negative for EHEC O111, EHEC O157, and other agents; ^d secondary infection cases; ^e of 86 cases, 18 were dual infection with EHEC O111 and O157; ^f could not be interviewed in detail; ^g asymptomatic cases.

Fig. 2.

Number of cases by (a) date of illness onset with outcome and (b) date of exposure in Toyama, Fukui, Ishikawa, and Kanagawa prefectures in 2011 (n = 86).

Fig. 3.

Pulsed-field gel electrophoresis analysis results. M_r, DNA size marker, Salmonella Braenderup strain H9812. Lane 1, patient 1, O111:H^–, VT1–, VT2–. Lane 2, patient 2, O111:H^–, VT1–, VT2+.