Food safety officials in New Zealand are urging people to cook raw mussels thoroughly after an increase in food poisoning.

New Zealand Food Safety reported a rise in people with food poisoning caused by Vibrio parahaemolyticus during the past six weeks.

A spokeswoman from the New Zealand Ministry of Health told Food Safety News that 28 Vibrio parahaemolyticus patients had been notified in the past six weeks but two infections were acquired overseas.

“Of the 26 cases, 22 confirmed and four under investigation, who acquired the disease in New Zealand, 21 of these have been linked to two outbreaks; 12 in Auckland region and nine in Bay of Plenty,” she said.

“Nearly two-thirds of cases are male. Cases range in age from 23 to 80 years. One third of them have been hospitalized and no deaths have been reported. Of the 26 cases acquired in New Zealand, 20 are known to have eaten raw/smoked/partially cooked mussels during the incubation period.”

Those ill live in Bay of Plenty (nine people), Waitemata (six), Counties Manukau (five) and Northland, Auckland, Waikato, Lakes, Taranaki and Nelson Marlborough (all one each).

Vibrio parahaemolyticus is a marine microorganism that occurs naturally worldwide. Not all strains cause illness in humans and surveys so far of New Zealand shellfish have found very low levels and incidence of disease-causing strains.

Patients ate raw or partially cooked mussels

Symptoms are predominantly stomach cramps and watery diarrhea and sometimes nausea, vomiting, and fever. Generally, people who are sick recover without hospital treatment, however, in severe cases hospitalization is required. New Zealand Food Safety advises consumers who are pregnant or have low immunity to avoid eating raw shellfish.

Cooking whole shell raw mussels until they open generally takes three to five minutes which is sufficient to achieve the 65 degrees Celsius for one minute required to ensure that any Vibrio parahaemolyticus present will be destroyed.

Paul Dansted, New Zealand Food Safety’s director of food regulation, said most people who became sick bought commercially-grown New Zealand mussels harvested from one growing area in the Coromandel and ate them raw or partially cooked.

“Additional testing is being done to confirm the type of Vibrio parahaemolyticus that has caused this illness. It is possible that the strain of Vibrio parahaemolyticus is unusually aggressive which may mean that even low numbers could cause illness. Additional testing of mussels and the waters that they are being grown in is also underway to help us understand why this has happened,” he said.

“The mussels at the center of the outbreak were all bought in their raw state, in the shell. They are not the mussels that can be bought in plastic bottles. Those mussels are cooked and marinated and are not affected. Until we have more information, New Zealand Food Safety is reminding people to take care when handling, preparing and consuming mussels.”

The growing area has been closed by New Zealand Food Safety while investigations continue.

New Zealand Food Safety advice includes:

  • Cooking temperatures for mussels should be above 65 degrees Celsius to ensure any Vibrio parahaemolyticus that is present will be destroyed.
  • Don’t eat raw or undercooked mussels or other shellfish
  • Always wash hands with soap and water after handling raw shellfish
  • Avoid contaminating cooked shellfish with raw shellfish and its juices

Campylobacter limit review

Meanwhile, the Ministry for Primary Industries (MPI) is reviewing regulatory limits for Campylobacter that apply to chickens for poultry operators.

There are three regulatory limits for Campylobacter in the Poultry National Microbiological Database Programme.

The Campylobacter performance target comprises the enumeration target; detection target; and prevalence performance target that only applies to standard throughput operators of meat chickens.

Options include maintaining the system as it is now, requiring reduced detections, removing the prevalence performance target, requiring a tighter enumeration target or amending reset of the non-compliant moving window. The preferred approach is a combination of these options.

“It is expected that lowering of all the targets (enumeration, detection and prevalence performance target) to some degree will prompt further actions by industry to reduce the levels of Campylobacter, and achieve nil detections of Campylobacter in a much more significant number of the total chickens processed in New Zealand,” according to New Zealand Food Safety.

MPI received a proposal to amend the Campylobacter regulatory limits from the Poultry Industry Association of New Zealand (PIANZ) in November 2018.

At the end of 2017, the total of notified campylobacteriosis cases was 6,482 and 3,771 are estimated to be foodborne. Attribution studies published in 2017 show that whilst there are other potential sources of foodborne Campylobacter such as raw drinking milk, poultry meat continues to be a significant source of human cases in New Zealand.

MPI is inviting comments on the discussion paper until Aug. 1, 2019.

  • Editors note: This article was updated on June 24 with the New Zealand Ministry of Health response

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