MOH-AVA Joint Press Release - Increase In Diarrhoea Cases Related To Raw Oyster Consumption

07 Jan 2004

There has been an increase in diarrhoea cases related to raw oyster consumption. From 13 - 31 Dec 2003, nine incidents involving 227 cases have been reported. The symptoms consisted of abdominal pain, watery stools, vomiting and fever. The illness was self-limiting and majority of the cases recovered following outpatient treatment or self-medication. Epidemiological investigations have revealed a significant association between illness and frozen half-shelled oysters from China that were consumed raw.

MOH has been working closely with AVA since the outbreak surfaced. The frozen half-shelf oysters have been traced to a consignment imported from China in Nov 2003. All remaining cartons of the oysters distributed to four seafood suppliers were recalled by the importer. Two other suppliers/importers of half-shell oysters have been asked to stop supplying to restaurants and hold all remaining stock for AVA's investigation.

AVA requires all imports of frozen oysters to be accompanied with a health certification issued by the relevant overseas authorities. In addition, AVA samples every consignment of frozen oysters and tests them for common food-borne pathogens. The consignment is only released for retail if the results are satisfactory.

However, satisfactory test results do not guarantee that the oysters are free from all pathogens that can cause diarrhoeal illness. As oysters are filter feeders, they can concentrate pathogens from their living environment. The pathogens can multiply to an infective dose that can cause gastroenteritis if the frozen oysters are not properly thawed or are displayed at room temperature for too long. Therefore outbreaks of diarrhoeal illness associated with consumption of raw oysters have been reported from time to time, even in the developed countries.

We would like to advise members of the public that there are risks associated with consuming raw or partially cooked oysters. Without adequate cooking, any pathogen which may be present will not be killed, and the person who consumes the oysters will be at risk of contracting hepatitis A and other food-borne diseases.

Anyone who has eaten raw or partially cooked oysters and subsequently developed food poisoning symptoms should seek medical treatment immediately.