Green salad with broccoli was what made more than 1,500  school students, teachers and staff members sick earlier this month in Iwaizawa, on Japan’s northern island of Hokkaido.

The Hokkaido Prefectural Government said Wednesday that broccoli salads prepared at the city’s central school kitchen on Feb. 9 tested positive for Salmonella that was a genetic match  of the bacteria confirmed in the case patients.

Because the bacteria were also found on utensils in a bowl used for mixing the salad, it is believed kitchen equipment may not have been sufficiently cleaned, or the salad may have been contaminated from chicken prepared nearby, according to a local official.

All of those who became ill were said to be recovering.