Food safety officials in New Zealand have again warned people not to eat raw mussels because of a risk of Vibrio infection.

Figures from the Institute of Environmental Science and Research (ESR) show a spike in illnesses, with 22 since the beginning of the year. This compares with 14 for the first three months of 2020, and four for the same period in 2019.

Earlier this month, New Zealand Food Safety warned consumers to thoroughly cook mussels before eating after two people became ill in the Nelson-Tasman region.

The agency is managing affected growing areas. All commercially harvested mussels from these areas must be cooked at a New Zealand Food Safety registered premises before sale or export.

Prevention tips
Paul Dansted, director of food regulation at New Zealand Food Safety, said Vibrio parahaemolyticus are naturally occurring bacteria found in seawater and occur when warmer temperatures during summer are favorable for growth.

“Symptoms of Vibrio parahaemolyticus may include watery or bloody diarrhea, abdominal cramps, nausea, vomiting, fever, and/or headache. The consequences can be more serious for people with weakened immunity, the young, the elderly and frail, and pregnant women,” he said.

“As undercooked mussels can be a risk factor, it’s important to take care with their preparation. To be safe to eat, thoroughly cook mussels at above 65 degrees C (149 degrees F) for one minute. This will ensure that any Vibrio parahaemolyticus present in the mussels will be destroyed.

“One good way to know when mussels are fully cooked is that their shells pop open when boiled or steamed, and the mussel inside is firm to the touch. It is raw mussels that we are advising against consuming. They are not the mussels that can be bought in plastic pottles. Those mussels are cooked and marinated and are not affected.”

Dansted also said people should store and refrigerate any leftover food for testing if possible.

People are also encouraged to wash their hands with soap and water after handling raw shellfish.

Symptoms usually occur within 24 hours of eating a contaminated product and last from one to seven days.

In 2019, an outbreak of Vibrio parahaemolyticus infection involved 24 people, of which two were hospitalized. It was linked to mussels and was the first such incident since 2009.

In June this past year there were eight confirmed cases of Vibrio parahaemolyticus associated with eating mussels harvested from two commercial areas in the Coromandel region.