Authorities in the United Kingdom and Ireland are investigating a foodborne outbreak suspected to be caused by norovirus in live oysters.

The oysters are thought to have come from Ireland and been purified in the UK and it is believed they are no longer on the market.

Harvesting records and purification operations at the unnamed implicated business in Ireland have been checked with nothing proving that oysters harvested at the time were contaminated.

A number of people fell ill in England and the investigation has pointed towards a potential norovirus outbreak linked to one restaurant.

The Food Safety Authority of Ireland (FSAI) told Food Safety News that it has sought detailed clarification on traceability and delivery channels.

“We have started investigations in relation to this notification from the Rapid Alert System for Food and Feed. It is not yet certain if the oysters that were consumed by the people who became ill were actually from Ireland,” said a spokeswoman.

“Nevertheless, at the request of the FSAI, the Sea-Fisheries Protection Authority (SFPA) checked the harvesting records and purification operations at the implicated business in Ireland. There is nothing to demonstrate that any oysters harvested at that time were contaminated. There are also no other reports of illness. The FSAI and the SPFA are continuing inquiries.”

High risk factors for shellfish-related norovirus include cold weather (low water temperatures), high prevalence of norovirus gastroenteritis in the community, and high rainfall (potentially leading to sewage system overflows). There is no regulatory limit for norovirus relating to shellfish.

The Food Standards Agency (FSA) advised consumers not to change their choice of eating out as a result of the outbreak.

“We are working with Public Health England to investigate why a number of people have reported digestive symptoms after eating out,” a spokeswoman told Food Safety News.

“This is being investigated as a potential norovirus outbreak linked to one restaurant. We’re working to determine the actual cause of the illnesses and which producer or supplier may be implicated.”

Norovirus can contaminate food and water and can also spread through contact with the feces or vomit of an infected person. It causes an estimated three million cases of diarrhea and vomiting each year and is estimated to be the third most common cause of foodborne illness in the UK.

Although symptoms can be unpleasant, it is considered a mild infection because it is usually short-lived and most people get better without medical treatment. Outbreaks have been caused by infected oysters and fresh produce such as berries and salad.

MPI shellfish warning

Meanwhile, the Ministry for Primary Industries (MPI) in New Zealand has extended a public health warning against collecting shellfish in the Northland east coast region due to a reported illness.

The affected area now covers from North Cape (Outo) south to Cape Karikari (Whakapouaka) and includes Parengarenga, Houhoura and Rangaunu Harbours.

One illness was noted in someone who consumed shellfish collected from Rarawa Beach. MPI is sampling and testing shellfish from this region. Results have shown levels of Paralytic Shellfish Poisoning (PSP) toxins above the limit of 0.8 mg/kg set by the agency.

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

Symptoms typically appear between 10 minutes and three hours after ingestion and may include numbness and a tingling (prickly feeling) around the mouth, face, and hands and feet, difficulty swallowing or breathing, dizziness, headache, nausea, vomiting, diarrhea, paralysis and respiratory failure.

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Photo of Joe Whitworth Joe Whitworth

Joe Whitworth is a food and beverage trade journalist. Prior to reporting for Food Safety News, he worked for William Reed Business Media since 2012 as Editor of Food Quality News before becoming food safety editor for Food Navigator. Whitworth has moderated sessions at Food Ingredients Europe in 2015 and The Ingredients Show in 2018. Before joining William Reed, he worked on newspapers run by Fairfax Media in Australia. Whitworth graduated with a journalism degree from the University of Central Lancashire (UCLan).