Outbreaks of norovirus in raw oysters and their management

Why risk management is required

Risk management of food incidents and outbreaks is a dynamic process, based on evidence and takes into account the individual circumstances of the incident. Although there can be common approaches, there is no “one size fits all” risk management approach.

Response to norovirus outbreaks 

In a norovirus outbreak situation, we will take into account all available evidence.  We generally recommend a 28-day pause in harvesting of oysters from the date the implicated batch was harvested, where epidemiological evidence links cases to the batch, and traceability information links it to a specific production area. This is to prevent further products, which are potentially contaminated, from being placed on the market. 

This is seen as a proportionate risk management approach given:

• the uncertainties in norovirus testing,
• a lack of a regulatory limit, and
• infectious norovirus is inactivated over time

Temporary closure of harvesting areas

Issuing a temporary closure notice is the responsibility of the relevant Local Authority or District Council. 

Withdrawal and recall of implicated oysters

As raw oysters are a live product with a short shelf-life, in outbreak scenarios there is often no implicated product remaining on the market by the time notifications of suspected illness are received.

FBOs are responsible for withdrawing and/or recalling any product that they suspect to be unsafe. Our guidance on food incidents, product withdrawals and recalls can assist FBOs.

Testing of oysters for norovirus 

There is a test method (ISO 15216), which can determine the level of norovirus in oysters, however, the limitation of this method is that it cannot differentiate between infectious and non-infectious norovirus. 

We do not currently use norovirus testing to inform our response during a norovirus outbreak. Further information is published in the policy response to the strategic risk assessment.  

Research testing of oysters for norovirus

Where oysters from batches implicated in an outbreak are available for testing, we support testing for research purposes as this may contribute to reducing uncertainties associated with the risk assessment.

Further Advice for FBOs

What are the symptoms of norovirus?

Although the symptoms of norovirus can be unpleasant, it is considered a mild infection. This is because it is usually short-lived and most people get better without medical treatment.

You are most likely to catch norovirus by coming into contact with an infected person but it can also be spread by contaminated food. 

The main symptoms of norovirus are:

• feeling sick (nausea)
• diarrhoea
• being sick (vomiting)

What can I do to stop norovirus from spreading in my food business?

As with most foodborne pathogens, maintaining good personal hygiene including effective hand washing can prevent transmission of norovirus to others.

Anyone working in food establishments should be fit for work. Staff with diarrhoea or vomiting should not return to work until they have had no symptoms for 48 hours.