Raw oysters

Eating raw oysters can lead to food poisoning. Be sure to prepare raw oysters carefully before you eat them.

Because oysters feed by filtering water, microorganisms and toxins may accumulate in their tissues. For example, oysters are sometimes contaminated by Vibrio bacteria.

Vibrio can be found in the coastal waters of Canada and the United States. They multiply faster in warmer water.

Water quality in shellfish harvest areas is monitored by the Canadian Shellfish Sanitation Program. Areas that pose a risk to human health are closed when needed. Oysters must be taken from areas that are open for harvest. Retailers are required to provide the area and date of harvest of the oysters they sell.

Most vibriosis cases occur in months when the water temperature is at its warmest. Eating raw oysters can lead to vibriosis at any time of year, no matter the harvest area. Oysters that contain Vibrio look and smell like safe oysters.

Who is at risk

Some people are more susceptible to foodborne illnesses. People with weakened immune systems, pregnant women, young children and the elderly should not eat raw oysters.

Low stomach acid caused by regular antacid use can also make people more.

Vibrio usually causes a mild illness that lasts for several days after the contaminated food is ingested. Symptoms of vibriosis can appear within hours and may include:

• Diarrhea
• Vomiting
• Stomach cramping
• Nausea
• Fever
• Headache

The illness may last longer and be more intense in vulnerable individuals.

To avoid intoxication, eat only fresh, living oysters. If an oyster shell is partially open and does not close when you touch it, the oyster is dead and must be discarded.

Keep living oysters in an open container at a temperature of 4°C or lower. Never put them in fresh water.

Before cooking or serving oysters, rinse the shell with drinking water to remove sand and dirt. Eat the oysters immediately once opened.

Lemon juice, hot sauce and alcohol do not kill microorganisms. The only effective way to eliminate them is to cook the oysters until the shell opens or the meat reaches an internal temperature of 74°C.

Cooking methods

Here are some recommended cooking methods, depending on how you’re going to eat your oysters.

Oysters in the shell

Boil the oysters until the shell opens, and keep boiling for 3 to 5 more minutes. You can also steam the oysters for 4 to 9 minutes.

Discard any oysters whose shell does not open while cooking.

Shucked oysters

Cook the oysters in boiling water for 3 minutes or until the edges curl. You can also fry them in oil at 190°C (375°F) for 3 minutes or bake them in the oven at 230°C (450°F) for 10 minutes.