TORONTO - Ontario's acting Chief Medical Officer of Health is warning that two dozen cases of gastrointestinal illness may be linked to oysters from British Columbia.

Dr. David McKeown says there have been 24 cases of gastrointestinal illness since January consistent with norovirus in people who reported eating raw or undercooked oysters.

McKeown says cooking oysters at an internal temperature of 90 degrees Celsius for a minimum of 90 seconds should eliminate norovirus and other potentially harmful microorganisms.

Foodborne outbreaks of norovirus can occur when food is contaminated with the virus. Health officials say shellfish such as oysters can become contaminated from the water before they are harvested.

The common symptoms of gastrointestinal illness are nausea, vomiting, diarrhea and stomach cramps which will last one to two days in healthy people.

Anyone experiencing these symptoms after eating oysters is urged to contact a doctor.