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Understanding the Food Safety Risks of Oysters

People enjoy oysters because they are tasty and nutritious. Uncooked oysters, however, are high-risk foods, and there are occasional reports of food poisoning outbreak related to the consumption of raw oysters in Hong Kong.

Oysters are filter feeders. They constantly draw in water and accumulate substances from it, including disease-causing microorganisms such as Vibrio bacteria, norovirus and hepatitis A virus, as well as chemical contaminants and natural toxins.

Eating raw oysters carries inherent food safety risks as there is no heat treatment to kill foodborne pathogens. Food poisoning cases related to raw oysters are reported locally from time to time. Although most of the patients suffer from mild symptoms such as diarrhoea, abdominal pain and vomiting, and recover on their own, raw oysters can also cause severe health consequences, especially in susceptible individuals.

Further, people are more likely to contract microorganisms with antimicrobial resistance ('superbugs') through eating raw or undercooked oysters. Whether or not 'superbugs' can cause illnesses, they may transfer their antimicrobial resistance genes to other bacteria inside the human body, therefore affecting the effectiveness of future use of antibiotics when needed.

Whichever type of oyster is purchased, consumers can ensure food safety by always following the steps below when choosing, storing, preparing, cooking and consuming oysters.

Shop from reliable licensed food premises, and choose fresh oysters with intact shells and without abnormal odour.
Check the expiry date of prepackaged shucked oysters, and ensure they are stored properly: at 4℃ or below for chilled products; at -18℃ or below for frozen products.
Once arrived at home, cook the oysters as soon as possible. Store the shucked chilled and frozen oysters properly at or below 4℃ and -18℃ respectively if not consumed immediately.
To prevent cross-contamination, raw oysters should only be placed in separate containers before being refrigerated and kept separate from cooked/ready-to-eat foods. Use different cutting boards and utensils to handle raw oysters and cooked or ready-to-eat food separately.
Wash hands thoroughly with liquid soap and running water for 20 seconds before and after handling raw oysters. Wear clean protective gloves when handling shell oysters to avoid injury and infection.
Wash shucked oysters thoroughly before cooking.
Cook oysters thoroughly to minimise the risk of foodborne diseases. Cook molluscan shellfish, including oysters, to an internal temperature of 90˚C for 90 seconds to minimise the risk of bacterial or viral infections.
Susceptible populations should avoid eating raw or undercooked oysters.
Avoid overindulgence in oysters and maintain a balanced diet for minimising the excessive exposure of chemical contaminants or natural toxins from a small range of food items.