A large norovirus outbreak led to the closing of at least thirteen elementary schools in the Japanese city of Hamamatsu last week, and over the weekend it became a really fascinating case from an epidemiological standpoint.
The first school closings began last Thursday, after at least 905 students and 40 staff from different schools were reported to have vomiting and diarrhea, beginning the night before. Aside from the closings, officials called for schools with at least 40 affected students to be tested and so far the virus has been found in 11 of 17 samples. Elementary and junior high schools in the area have also been instructed to disinfect their facilities with bleach.
School lunches were considered as a common factor because so many people became sick at once, and officials ordered the local schools to not serve lunches for four days as a precaution. By Saturday, a bread-making company was identified as a likely source of the outbreak, and the city closed the company’s plant after the virus was detected on material in the facility. Some of their bread had been delivered to the schools earlier in the week, and over the weekend three of the plant’s 23 workers tested positive for norovirus (along with 13 that have so far tested negative). The three people had also been in direct contact with the bread that had been shipped to the schools.
It is particularly interesting because the three workers had not shown any symptoms and may have been serving as asymptomatic carriers of the virus. This is always a concern and can understandably make tracking and controlling outbreaks more difficult. They were sent home for three days as a precaution, and the company has begun a recall of its products.
The investigation is still ongoing and we will provide updates to this post as more information becomes available.
Jan. 22 UPDATE: Fourteen of the fifteen schools that were ultimately closed reopened today, and the remaining school is expected to reopen tomorrow. The students were shown videos of how to properly wash their hands and it was reported that many came to school in face masks as a precaution. The Hamamatsu city government decided to reopen the schools when less than 5% of the students were sick, and the area schools will not be serving lunches until this coming Monday.