Category Archives: Microbiological Risk Assessment

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Raw Oysters are High-risk Foods
Oysters are filter feeders. They constantly draw in water and accumulate materials from water, including pathogens such as Vibrio bacteria, norovirus and hepatitis A virus. These pathogens can infect people who eat oysters raw or undercooked. In addition, bacteria like Vibrio can continue to grow in oysters after harvesting if oysters are not maintained at low enough temperatures from harvest through to consumption. Food poisoning outbreaks related to raw oysters have been reported locally from time to time. Although the illness is usually mild and self-limiting, causing symptoms such as diarrhoea, abdominal cramps and vomiting, they can also cause severe health consequences especially for susceptible individuals.

Additional Risks in Shucked Oysters
Both physical and microbiological contamination are possible during the shucking of oysters. Physical removal of shellfish meat from the shell at the shucking table often exposes the product to dirt, mud and detritus. Shucked oysters should be rinsed or washed well to eliminate these contaminants and to reduce microbiological level of the products. Good hygiene practices should also be observed to minimise contamination from the workers and the working environment.

Before deshelling, oysters can stay alive even after long-haul shipping if kept under correct temperature and conditions. Once killed after shucking, raw oysters can deteriorate quickly if the temperature is not low enough to limit bacterial growth. Shucked oysters should be packed and chilled or frozen as soon as possible. Furthermore, an uninterrupted cold chain during transportation is critical to ensure safety and quality of the shellfish products.