Health Canada would like to remind Canadians that raw shellfish – such as oysters, clams, scallops, mussels and cockles – can carry bacteria, viruses and toxins that can cause foodborne illness if they are not harvested, stored, handled or prepared appropriately.
Note: Recently there have been several warnings and advisories related to shellfish:
• Illnesses associated with eating raw or undercooked shellfish reported in British Columbia
• Safety recommendations for eating shellfish in New Bruswick
• Live and raw shellfish imported from Korea should NOT be consumed
The following information was adapted from a recent Health Canada publication.
Shellfish is a nutritious food choice. As with all foods, it is important to store, handle and prepare shellfish appropriately to help prevent illness. In particular, children, pregnant women, seniors and people with weakened immune systems are more susceptible to foodborne illness and should avoid eating raw or undercooked shellfish.
Here are some steps you can take to prevent foodborne illness from bivalve shellfish:
(1) Buy shellfish from reputable sources, and keep them cold (below 4°C). A retailer selling raw shellfish should be able to show you a shellfish shipper's tag.
(2) Refrigerate immediately after purchase. Do not put live shellfish in a closed container or into fresh water. Cover the shells with a damp cloth and place on the lowest shelf of the refrigerator. Store shucked (opened) shellfish in a closed container. Raw shellfish can be kept refrigerated for a few days, depending on their freshness and quality, and can be stored in the freezer for 2-4 months. Shucked oysters should be frozen if you do not eat them within two days.
(3) Check the packaging on frozen shellfish. Make sure that the packaging is not torn or open and that there is minimal frost or ice crystal formation on the packaging. Too much frost could mean that the shellfish has been frozen for a long time or has been thawed and refrozen. Place the frozen shellfish in the freezer immediately after purchase until you are ready to use it. You should never defrost shellfish at room temperature. Thaw food in the refrigerator, in cold water, or in the microwave if you will be cooking it immediately. If thawing in cold water, replace water every 30 minutes.
(4) Keep raw shellfish separate from cooked foods and follow good hygiene practices: wash hands before preparing foods, wash hands after handling raw shellfish, and wash counters and utensils with soap and warm water after preparation.
(5) Make sure your shellfish is fresh. Fresh oysters, clams, scallops, mussels and cockles should have tightly closed shells or they should close their shells when you tap them.
(6) Shucked oysters (usually sold in tubs) are not meant for raw consumption.
(7) It is best to cook oysters, clams, scallops, mussels and cockles to minimize the chances of foodborne illness. Guidelines for cooking bivalve shellfish are:
• Boil oysters, clams, scallops, mussels and cockles until the shells open, and then boil for an additional 3-5 minutes. You should also boil or simmer shucked shellfish for at least 3 minutes or until the edges curl.
• Steam for 4-9 minutes and throw out those that did not open.
• Fry for at least 3 minutes at 190ºC (375ºF).
• Bake for at least 10 minutes at 230ºC (450ºF).
(8) If you wish to harvest shellfish yourself, make sure you do so in areas that are open for harvesting. Chemical contaminants or natural toxins from marine algae could be present in shellfish any time of the year, and cooking will NOT destroy these toxins. Contact your nearest Department of Fisheries and Oceans office listed in the blue pages of your local telephone directory for information on areas currently open for shellfish harvesting. You may also want to check with your local or provincial government about harvesting restrictions or consumption advice for shellfish not purchased from commercial establishments.
It is estimated that there are approximately 11 million cases of foodborne illnesses in Canada every year. Many of these illnesses could be prevented by following proper food handling and preparation techniques.
If you have any abnormal symptoms or feel ill after eating shellfish, consult your physician immediately.
More information about shellfish food safety is available from:
• Healthy Canadians - Shellfish Food Safety
• Canadian Food Inspection Agency – Marine Toxins in Bivalve Shellfish
• Canadian Partnership for Consumer Food Safety Education – Be Food Safe
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