Nine cases of Norwalk virus have been confirmed on P.E.I. in the last few weeks, and the province's chief health officer believes hundreds of others could be suffering from it.

Norwalk is a gastrointestinal illness that causes vomiting and diarrhea.

"It is fairly contagious," said chief health officer Heather Morrison.

"Usually symptoms have a very sudden onset. The symptoms usually appear within one or two days after exposure to the virus. But you can certainly protect yourself if you have thorough hand washing."

Morrison said there have been no new cases confirmed in the last few days, but the large majority of Norwalk cases are not reported.