What are the main foods implicated?
Most foodborne illness outbreaks due to norovirus in France are related to the consumption of contaminated shellfish, in particular oysters eaten raw.
To a lesser extent, mixed dishes such as sandwiches or mixed salads and certain fresh produce eaten raw, such as berry fruits, can also cause poisoning.
What are the health impacts?
Norovirus causes acute gastroenteritis lasting an average of 2 to 3 days without complications. In children and the elderly, the symptoms may persist for longer.
Norovirus in figures
Noroviruses are responsible for one third of foodborne infections in France. With an estimated 516,000 cases per year, they are associated with 20% of hospital admissions due to such infections.
How is this virus transmitted?
There are several routes of transmission of the virus:
- by the faecal-oral route:
- Directly, from person to person, this is the main route of transmission,
- Indirectly, through ingestion of contaminated food or water or from contact with a contaminated environment such as surfaces. Foodborne transmission can then be amplified by person-to-person transmission.
- by air, via aerosols during vomiting.
Are these viruses seasonal?
Noroviruses are the main viruses responsible for winter gastroenteritis outbreaks. In Europe, these viruses circulate mainly in winter and early spring.
How can consumers limit their exposure?
- Wash hands thoroughly with soap after using the toilet, and before preparing and eating meals,
- Avoid preparing meals if you have gastroenteritis symptoms,
- Only consume shellfish from an authorised and monitored production area. This is the case with any shellfish purchased in shops,
- For recreational fishing, comply with the non-consumption recommendations issued in certain zones (ask at the town hall or look on the internet). In the absence of information, it is preferable that shellfish be cooked thoroughly before consumption,
- Fruit and vegetables eaten raw should first be thoroughly rinsed with drinking water.
What is the source of norovirus in food?
Infected humans form the only reservoir of noroviruses. When an individual has norovirus gastroenteritis, the virus is shed in large quantities in faeces. During winter gastroenteritis outbreaks, the number of patients is high and there is significant release of the virus into wastewater. Noroviruses are highly resistant in the environment. Wastewater is collected and treated in sewage treatment plants.
In the event of heavy rainfall or accidental discharge (private households that are not connected to mains drainage ), wastewater discharges that may be undiluted can reach coastal areas, and even shellfish farming areas.
The virus does not multiply in the environment or in oysters. However, oysters concentrate viruses, and the viral load is sometimes sufficient to generate cases of infection in humans.
Fresh produce can be contaminated by irrigation water loaded with virus particles, but also during hand-picking.
Foods can also become contaminated during handling by an infected person who does not take the appropriate hygiene precautions. This potentially concerns any type of food that is handled and then consumed raw or undercooked.
What is ANSES's role?
The Agency is responsible for assessing the risks and identifying measures to control this virus at all stages of the food chain: production, handling, consumption.
It is also the National Reference Laboratory (NRL) for foodborne viruses in foodstuffs of animal origin (excluding shellfish).