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Korean oysters consumed raw may cause illness

The New Zealand Food Safety Authority (NZFSA) is reminding people not to consume uncooked oysters imported from Korea. All bags of frozen Korean oysters are clearly labelled as requiring to be cooked before consuming. This product is known to sometimes carry norovirus, which causes a gastrointestinal illness.

The Korean oysters are packed frozen in 1kg bags and distributed throughout New Zealand, and labelled, as is required by the current import health standard, with a statement that the product must be cooked or must not be eaten raw.

They must be cooked in such a way that the centre of the oyster reaches 90ºC and is held at that temperature for 90 seconds. NZFSA also reminds chefs and consumers using the product to take particular care with hand and kitchen hygiene, particularly when defrosting, to ensure that other foods are not cross-contaminated with raw oyster juice.

Typically, symptoms of norovirus infection include headache, nausea, vomiting, abdominal pain and diarrhoea and occur between 10 and 50 hours after consumption. Symptoms usually resolve in two days. Those affected should avoid preparing food for at least 48, and preferably 72, hours after the last symptoms have ended. Norovirus is very contagious, and infected food handlers can be a major source of infection.

In the recent outbreaks, the label instructions appear not to have been followed. NZFSA is reviewing the import health standard to determine if the current provisions are sufficient and is considering if further risk mitigation steps are needed. NZFSA is also approaching the Korean government agencies responsible for the certification of these products to discuss what assurances New Zealand will need to have confidence that product arriving in New Zealand is as stated.

There is more information on this topic at

Frozen Korean Oysters – Questions and Answers

What are noroviruses?

Noroviruses are members of a group of viruses called caliciviruses also known previously as 'Norwalk-like viruses'. Infection with norovirus affects the stomach and intestines, causing an illness called gastroenteritis, or 'stomach flu'. The disease is self-limiting and characterised by nausea, vomiting, diarrhoea, and abdominal pain. Headache and low-grade fever may occur. The infectious dose is unknown but presumed to be low. Gastroenteritis from a norovirus is contagious. Noroviruses are relatively hardy and can survive freezing to relatively high cooking temperatures, as well as high levels of acids. They also can survive chlorination up to 10ppm.

What is being done to ensure that people do not misuse the product and cause further norovirus outbreaks?

NZFSA is reminding people to follow the instructions on the package which state that the oysters must be cooked before consumption and are not suitable to be eaten raw. As with all foods, it is the responsibility of those preparing food to ensure that proper and appropriate food handling is followed. In the case of this product, the warning on the label must be taken into account. NZFSA is also considering other risk management options

How do I know when the oysters have been cooked enough to be safe?

Korean oysters need to be fully thawed before cooking, and then cooked with an internal temperature of at least 90 degrees Celsius for 90 seconds or more. This means that these oysters may not suitable for many recipes. It is possible that pan and deep frying oysters may not be suitable as the internal temperature may not be high enough for long enough. Stocks, stews and chowders, and inclusion in pies and other baked dishes with long cooking times are more likely to be effective.

What else do I need to know if I want to safely use this product?

Care must be taken when thawing, washing and preparing these oysters before cooking. The juices may contain norovirus, and this can easily contaminate other foods unless proper hand washing and hygiene practices are followed. The 4Cs and the 20+20 rule should be followed:

• 4Cs – clean, cook, cover, chill

• 20+20 rule – 20 seconds hand washing with plenty of soap, then 20 seconds thorough hand drying using a clean towel or disposable paper towels.

Ensure that work surfaces, kitchen equipment and utensils are thoroughly cleaned with soap and hot water after contact with raw oysters.

If Korean oysters are contaminated, why are they on sale?

No food is 100% safe for all people all the time, and this is especially the case with animal products such as meat and seafood. Korean oysters have been implicated in norovirus outbreaks and a requirement was made in 2003 for packages to be clearly labelled with a notice that the product should be cooked before consumption.

In recent outbreaks, those label instructions appear not to have been followed. NZFSA is reviewing the import health standard to determine if the current provisions are sufficient and is considering if further risk mitigation steps are needed. NZFSA is also approaching the relevant government agencies in Korea responsible for the certification of these products to clarify the validity of the certificates that accompanied the imported products and will be addressing what further assurances New Zealand will need to have confidence that product arriving in New Zealand is fit for purpose.

Following the label directions to cook the product reduces any risk of infection to 'nominal zero' (being so small as to be indistinguishable from a zero risk). NZFSA is not aware of any instances of norovirus infection from properly cooked Korean oysters.


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