Vancouver Coastal Health has asked restaurants to take increased precautions when serving oysters as more illnesses are reported.

Public health officials have ordered eateries to cook all oysters harvested from B.C. waters and to only serve oysters from outside the province raw.

The order was issued in response to a naturally occurring bacterium found in B.C.'s coastal waters that causes a
gastrointestinal illness.

The health advisory says 31 cases connected to raw oysters within Vancouver Coastal Health have been reported so far this year, although the actual number of illnesses is expected to be much higher because not all cases are reported.

Symptoms include diarrhea, cramps, vomiting and fever that can last up to a week.

The public is also advised to cook oysters harvested in B.C., or if they want to consume raw oysters to ensure they've been harvested from outside provincial waters.