SA Health warns of a spike of gastro cases linked to uncooked oysters

It’s enough to make you feel queasy – a spike in bacterial infections has been linked to uncooked seafood, as cases of gastro quadruple in two years.

A spike in food-related illness cases has been linked to uncooked oysters, with the number of cases quadrupling since 2019.

Infections of the bacteria vibrio parahaemolyticus have increased from eight cases in 2019 in South Australia to 36 confirmed cases so far this year. There were no confirmed cases in 2020.

Joanne Cammans, SA Health’s acting director of Food and Controlled Drugs, said the bacteria was linked to uncooked oysters and had serious consequences for vulnerable members of the community.

“This increase in cases reported to us in such a short period of time is very concerning, as foodborne illnesses can be quite serious for more vulnerable people in our community, such as older South Australians, pregnant people and people with compromised immune systems,” she said.

“People with lowered gastric acidity, such as those who are taking antacids, and people with liver disease are particularly vulnerable to vibrio parahaemolyticus and so should avoid eating raw oysters.

Raw oysters in the shell. Photo: Rob Wright

The bacteria causes gastro-like symptoms including watery diarrhoea, abdominal cramps, nausea, vomiting, fever and headaches, usually within 24 hours of eating the contaminated food.

“The infection can be acquired by eating undercooked shellfish and fish, however raw oysters are often the most common cause,” she said.

The Department of Primary Industries and Regions said they were investigating reasons for the outbreak but international research had yet to pinpoint why there was an increase this year.

“Inspections by PIRSA officers have found that food safety practices are being appropriately applied on farm,” executive director of PIRSA biosecurity said.

“Raw unshucked oysters should be stored at less than 10C and shucked oysters at less than 5C to minimise the risk of vibrio parahaemolyticus infection.”

Seafood eaten raw or ready-to-eat cold cooked prawns or cold smoked salmon, are not recommended for pregnant women, people with reduced immune systems or older people because of the risk of bacterial infections.