A full 25 percent of the student body at Tofta high school, in southern Sweden, have been hit with the gastrointestinal bug, norovirus, according to a The Local report Tuesday.


Some 150 students and 23 school staff have been affected.

“It struck last Friday but now I’m back at work,” headmaster Tobias Fahlén told the local press. The source of the outbreak is not known.

Per instruction from health officials, the school performed extra cleaning and sanitizing of the kitchen and bathrooms.

Norovirus peaks in February in Sweden, the report notes.

Norovirus is a highly contagious viral illness that often goes by other names, such as viral gastroenteritis, stomach flu, and food poisoning.

The symptoms include nausea, vomiting, diarrhea, and some stomach cramping. Sometimes people additionally have a low-grade fever, chills, headache, muscle aches, and a general sense of tiredness. The illness often begins suddenly, and the infected person may feel very sick. In most people, the illness is self-limiting with symptoms lasting for about 1 or 2 days. In general, children experience more vomiting than adults do.

Norovirus is spread person to person particularly in crowded, closed places. Norovirus is typically spread through contaminated food and water, touching surfaces or objects contaminated with norovirus and then putting your hand or fingers in your mouth and close contact with someone who is vomiting or has diarrhea.