Norovirus in Shellfish

What is norovirus?

Norovirus is a highly contagious virus that can cause viral gastroenteritis, often called "food poisoning" or the “stomach flu.” Eating raw or partially cooked shellfish can cause norovirus infection.

How do shellfish become contaminated with norovirus?

Norovirus makes its way into the marine environment through untreated human sewage (poop) and vomit. This may come from leaky septic systems, faulty waste water treatment plants, boaters, or beach-goers. Shellfish are filter feeders, which means they filter seawater through their bodies to get food floating in the water. When norovirus particles are in the water, shellfish can accumulate the virus in their bodies.

What types of shellfish are affected?

All bivalve shellfish such as clams, geoducks, mussels, scallops, and oysters can transmit norovirus. Illness outbreaks are most often linked to oysters because they are commonly eaten raw.

What are the symptoms of norovirus?

The most common symptoms of norovirus are stomach pain, projectile vomiting, and severe diarrhea. Other symptoms may include fever, headache, and body aches. Some people can be infected with norovirus and have no symptoms. Good hygiene and hand washing, especially after using the bathroom and when handling food, are important to help limit the spread of norovirus.

How soon do symptoms appear?

Symptoms usually appear 24-48 hours after being exposed to the virus. Sometimes symptoms appear as early as 12 hours after exposure. Most people recover in 1 to 3 days.

Who is most at risk?

Anyone can get norovirus. Young children, the elderly, and anyone who already has other illnesses may experience longer, more serious illness, and rarely, death.

People who eat raw oysters or undercooked shellfish are at higher risk of a norovirus illness. Norovirus persists longer in colder marine water and we tend to see more shellfish-related norovirus illnesses in November through March.

How can I protect my family from shellfish-transmitted norovirus?

What should I do if I think that I or someone in my family has contracted norovirus from eating shellfish?

How can I help prevent the spread of norovirus in the marine environment?

The best way to prevent norovirus in the marine environment is to manage human waste responsibly.

Are there other illnesses associated with eating shellfish?

Yes. Eating undercooked shellfish can cause a bacterial infection called vibriosis. Marine biotoxins, which are not destroyed by cooking, can cause Amnesic Shellfish Poisoning, Paralytic Shellfish Poisoning and Diarrhetic Shellfish Poisoning. Some people can have an allergic reaction to shellfish.

More Resources

Norovirus Questions and Answers

Biotoxins and Shellfish-Related Illnesses

Prevent Shellfish-Related Illnesses