Oysters behind norovirus outbreak in New Zealand

Norovirus outbreak linked to oysters

The Ministry for Primary Industries (MPI) in New Zealand has warned people not to eat certain brands of chilled oysters as they may be contaminated with norovirus.

Matakana Oysters, Orata Marine, Seafood Harbour and Hutchings and Addison are recalling all oysters harvested from the Mahurangi Harbour, north of Auckland from mid-January.

The ministry was alerted by local health authorities as 11 people became ill after eating oysters from the area. 

Samples were tested by the Institute of Environmental Science and Research (ESR) and norovirus was found. The type of virus was the same as that in the affected people.

Short shelf life

MPI said batch numbers and brand names were not confirmed but details will be posted on the website as they become available.

The products are not exported. Most are sold in the local area in pottles or on the half shell.

Melinda Sando, MPI’s manager of food compliance service group, said the amount of affected product is likely to be small due to the very short shelf life.

“Our main concern, however, is that people may have frozen the oysters and still have them in their freezer. It is very important that they are discarded.”

Sando said the problem appears to be limited to a small area of the harbour around Dyers Creek.

“It is likely to be the result of a localised contamination – for example discharge from a boat or a leaking septic tank.”

MPI has also halted harvesting of oysters from the harbour, near Warkworth north of Auckland.

Norovirus gastroenteritis symptoms include vomiting followed by diarrhoea.

The ministry advised people who have eaten affected oysters to see their GP if symptoms are severe or persistent or if they are unable to keep hydrated.

PSP toxin warning

MPI has also warned against collecting or eating shellfish harvested from the Bay of Islands - Cape Brett north to Cape Wiwiki.

Routine tests on shellfish samples have shown Paralytic Shellfish Poisoning (PSP) toxins at what the agency called ‘levels of concern’. The safe limit is less than 0.8mg/kg.

Cooking or freezing shellfish does not remove the toxin. PSP is caused by a group of chemicals called the saxitoxins and gonyautoxins.

Symptoms typically appear between 10 minutes and three hours after ingestion.

Mussels, oysters, tuatua, pipi, toheroa, cockles, scallops, catseyes, kina (sea urchin) and all other bivalve shellfish should not be eaten.

Pāua, crab and crayfish may be eaten if the gut has been completely removed prior to cooking, as toxins accumulate in the gut.

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