More than 30 people have fallen sick in the past few months with Vibrio infections in New Zealand.

Due to the increase in Vibrio parahaemolyticus cases around the country this summer, New Zealand Food Safety has reminded consumers to thoroughly cook mussels.

Since mid-November 2021 — which is summer in the Southern Hemisphere country — there have been 31 confirmed patients and 10 people have been hospitalized.

Impact of changing conditions
Vince Arbuckle, deputy director-general at New Zealand Food Safety, part of the Ministry for Primary Industries (MPI), said evidence suggests a change in water temperature and conditions may make live mussels more susceptible to the bacteria.

“As mussel harvesting is a favorite summer pastime of many New Zealanders and they are sold live and raw in many New Zealand supermarkets, we advise consumers to cook mussels thoroughly before consumption to avoid getting sick,” he said.

“We have been working with the major supermarket chains to ensure that point-of-sale signage to cook mussels is available for consumers. New Zealand Food Safety is working together with public health units and the seafood industry to ensure appropriate public health measures are taken. However, consumers can minimize risks by cooking their shellfish thoroughly.”

Those with low immunity and pregnant or elderly people in particular should avoid eating raw or undercooked shellfish as the illness can be more severe, according to public health officials.

Guidance and past incidents
Advice from New Zealand Food Safety includes washing hands and kitchen utensils after handling raw seafood, and before using other utensils or handling other foods.

The agency also recommends refrigerating shellfish as soon as possible after harvesting from the beach or buying from the supermarket. Mussels should be stored in a bowl covered with a cold, wet towel on the bottom shelf of the refrigerator.

One way to know mussels are fully cooked is that their shells pop open when boiled or steamed and the mussel inside is firm to touch.

Figures from the Institute of Environmental Science and Research (ESR) showed 22 Vibrio illnesses from the start of 2021 until March of that year. This compares with 14 for the first three months of 2020, and four for the same period in 2019.

In June 2020, there were eight confirmed cases of Vibrio Parahaemolyticus associated with eating mussels harvested from two commercial areas in the Coromandel region.

In 2019, an outbreak of Vibrio parahaemolyticus linked to mussels involved 24 people, of which two were hospitalized.

Symptoms of Vibrio parahaemolyticus may include watery or bloody diarrhea, abdominal cramps, nausea, vomiting, fever, and headaches. They usually occur within 24 hours of eating a contaminated product and last from one to seven days.

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