Risk factors for sporadic shiga toxin-producing escherichia coli O157 infections in Japan

Backgrounds: Shiga toxin-producing Escherichia coli (STEC) infection is one of the major international public health concerns. Recently in Japan, the total number of STEC cases reported from both outbreaks and from sporadic infections was approximately 3000-4000 annually. We have not have conducted efficient preventive measures yet. This study was to determine the risk factors for sporadic case of STEC O157 infection in Japan.

Methods: This study conducted a matched case control study. Case defined as a person presenting with at least one acute gastroenteritis symptom (diarrhea, bloody stool, abdominal pain, vomiting) and with isolation of the STEC O157 from five local prefectures in 2010. Possible outbreak-related cases were excluded. Matched odds ratios (OR) was calculated by using conditional logistic regression.

Results: The obtained numbers of sporadic case of STEC O157 infection and control were 53 and 221, respectively. Female (67.9%) was higher than male (32.1%). The highest age group was 18-39 years old (37.7%) and the next was 6-17 years old (24.5%). The proportion of the symptom of abdominal pain, diarrhea and bloody stool were 88.7%, 88.7% and 73.6%, respectively. Infection with STEC O157 was significantly associated with the consumption of the raw beef meat (OR=13.3, 95% confidence interval (95%CI):4.4-39.8), raw beef liver (OR=28.2, 95%CI:3.0-infinity) and beans sprout (OR=10.5, 95%CI:1.6-69.4). Environmental exposures and contact with animals were not significantly associated in this study.

Conclusions: We concluded that raw beef meat, raw beef liver and beans sprout were important risk factors and targeted control measures with high priority for the sporadic STEC O157 infection in Japan.