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?
- Shellfish Safety Map - Check for beach closures and advisories before you harvest.
- Cook Your Shellfish - Cook shellfish until it reaches an internal temperature of at least 145° F and follow our guidance for cooking different types of shellfish. Quick steaming isn't sufficient to kill norovirus. Avoid eating raw and undercooked shellfish.
What should I do if I think that I or someone in my family has contracted norovirus from eating shellfish?
- Contact the local health department where you live. This helps health authorities track illnesses so they can close shellfish harvest areas when appropriate.
- Stay home, rest, and drink plenty of fluids to prevent dehydration. Sick children should stay home from school or childcare. Food workers with vomiting or diarrhea may not go to work until at least 24 hours after symptoms go away. If the illness lasts more than a few days and becomes severe, see a local healthcare provider. There's no vaccine and no medication to treat norovirus.
- Try to limit contact with other household members. Norovirus spreads very easily through person to person contact and you may be contagious from the moment you feel sick until up to 2 weeks after you have recovered.
- Norovirus lives on surfaces for several days. Disinfect surfaces contaminated with poop or vomit and areas or objects that a sick person has touched. Many household cleaners don't kill norovirus. Use a store-bought product from EPA's Registered Products Effective Against Norovirus (PDF) or make your own household bleach solution following these recommendations:
- 1 tablespoon of bleach per gallon of water for stainless steel, food/mouth contact items, and toys.
- 1/3 cup of bleach per gallon of water for non-porous surfaces such as tile floors, counter-tops, sinks, and toilets.
- 1½ cups of bleach per gallon of water for porous surfaces such as wooden floors.
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.
- If you have a septic system, make sure it is regularly inspected and maintained.
- Don't vomit or poop on the beach. Find the nearest bathroom and use it before you go out to the beach.
- Don't vomit or poop off of your boat. Empty your boat's sewage holding tank at a pump-out station. If you don't have a holding tank or porta-potty, use a sealable bucket that you can empty in an appropriate facility on land.
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.
Norovirus Questions and Answers
Biotoxins and Shellfish-Related Illnesses