More than 1,000 students and teachers in northern Japan have been sickened by food poisoning — and school lunch is being blamed.

Officials say more than 800 students at nine schools in Iwamizawa City have missed classes after developing diarrhea, vomiting and fever. Some schools will be closed until Sunday. The sickness tally rose to 1,048 on Tuesday.

City official Naomi Kurata says doctors suspect school lunches were contaminated with salmonella after detecting the bacteria in many of the patients.

Health officials are investigating lunch samples from last week and how they were stored. Kurata says a likely culprit is Thursday’s meal — turnip with ground chicken, soybean soup with sliced potatoes, green salad, rice and milk.