A Large Outbreak of Gastrointestinal Infections Associated with Escherichia coli and Consumption of Milk Served in 25 schools in Toyama, Japan, June 2021

Severe foodborne disease outbreaks occurring in the school setting are a major public health issue. On June 17, 2021, Toyama City Public Health Center received a report of a suspected outbreak of food poisoning from the Board of Education of Toyama City. The board reported that 459 students and 5 teachers were absent from school or left early on June 17. We investigated the suspected outbreak and examined the implementation of control measures in a small-scale milk processing company linked to the outbreak. In particular, we performed an epidemiological investigation involving a traceback and traceforward investigation, an inspection of the processing company, a microbiological analysis, a hazard analysis, and an evaluation of critical control points. In total, 1,896 individuals developed at least one gastrointestinal symptom and were absent from school and/or left early. In total, 25 schools and childcare facilities were affected. The epidemiological investigation showed that consumption of school lunch milk from a specific milk company was significantly associated with absence from school on June 16-18, with odds ratios ranging from 2.2 to 21.7. No cases were linked to other distribution facilities. Milk and stool samples yielded Escherichia coli of undetermined pathotype. The milk processing facility had 20 hazards, including the heat treatment machine. The facility did not undergo routine checks and maintenance. The temperature detector sensor was manufactured to have 20 copper wires, but just 2 wires were intact, leading to a possible overestimation of temperature. We recommended that the facility routinely measure direct temperature and implement checks and maintenance of the heat treatment unit.