More than 400 school children called in sick to schools on Friday in a suspected case of mass food poisoning in the western Japanese city of Hiroshima, where the municipal education board launched an investigation into the virulence factors to determine the cause of illness, local press reported.

The Hiroshima City Board of Education reported that a total of 415 students from 10 junior high schools in the city exhibited gastroenteritis symptoms of vomiting and diarrhea, and were unable to attend to their classes on Friday. All afternoon classes at the schools were canceled.

According to Nippon Hoso Kyokai (NHK), Japan’s public broadcaster, all pupils at the 10 schools eat school meals supplied by the same catering company based in the city. The symptoms were caused by viruses such as norovirus, which has caused mass outbreaks of infectious gastroenteritis over the past few weeks in schools and hospitals in Japan.