California health officials say about 100 people statewide have contracted norovirus in the past week after eating raw oysters from British Columbia, Canada.

The state Department of Health issued a warning Wednesday about the possible risk of illness from consuming oysters harvested in south and central Baynes Sound.

Canada has reported more than 170 cases of gastrointestinal illness linked to consumption of raw oysters.

Officials say the number of new illnesses is declining but the investigation is ongoing.

Four oyster farms in British Columbia’s Baynes Sound that were linked to illnesses remain closed.

Norovirus is contagious and causes inflammation of the stomach and intestines. Symptoms include vomiting, diarrhea and fever.