Noroviruses (Norwalk viruses)

What are noroviruses?

Noroviruses belong to a family of viruses that cause the "stomach flu." Noroviruses are also called Norwalk-like viruses and caliciviruses. Stomach flu is also called gastroenteritis, food infection, food poisoning, and acute nonbacterial gastroenteritis.

What causes infection with noroviruses?

Noroviruses generally spread through contaminated water and foods, although they can also pass from person to person. You may become infected by:

  • Eating foods or drinking liquids that are contaminated with norovirus. Shellfish and salad ingredients are the foods most often infected with the viruses. Food other than shellfish may be contaminated by food handlers.
  • Touching surfaces or objects contaminated with norovirus, and then placing your hand in your mouth.
  • Having direct contact with someone who is infected. For example, if you are a caregiver or share foods or utensils with someone who is ill, you may become infected.

Persons working in day care centers or nursing homes should pay special attention to children or residents who have norovirus illnesses. This virus is very contagious and can spread rapidly throughout these environments.

What are the symptoms?

The symptoms of gastroenteritis caused by the noroviruses include nausea, vomiting, diarrhea, and abdominal pain. Diarrhea and vomiting can cause dehydration. You may have a headache and fever of less than 100°F (37.8°C). A mild and brief illness usually develops 24 to 48 hours after you eat or drink the contaminated food or water and lasts for 24 to 60 hours. Most people are rarely very sick or have to go to the hospital.

How are infections with noroviruses diagnosed?

Since most norovirus infections are mild and pass in a few days, most people do not go to their health professionals for a diagnosis. You can often diagnosis food poisoning yourself if others who ate the same food as you also become ill.

If you do go to your health professional, he or she will make the diagnosis based on your symptoms, a medical history, and a physical exam. Your health professional will ask where you have been eating and whether anyone who ate the same foods has the same symptoms. A stool test is sometimes done.

How are infections with noroviruses treated?

You treat gastroenteritis caused by noroviruses by managing any complications until it passes. Dehydration caused by diarrhea and vomiting is the most common complication. Do not use medicines, including antibiotics and other treatments, unless your health professional recommends them.

To prevent dehydration, take frequent sips of a rehydration drink (such as Lytren, Pedialyte, or Rehydralyte). Try to drink a cup of water or rehydration drink for each large, loose stool you have. You can also use a sports drink, such as Gatorade. Soda and fruit juices have too much sugar and not enough of the important electrolytes that are lost during diarrhea, and they should not be used to rehydrate. In cases of severe dehydration, fluids may need to be replaced through an IV (intravenously).

Try to stick to your normal diet as much as possible. Eating your usual diet will help you to get enough nutrition. Doctors believe that eating a normal diet will also help you feel better faster. But try to avoid foods that are high in fat and sugar. Also avoid spicy foods, alcohol, and coffee for 2 days after all symptoms have disappeared.

How can you prevent infection with noroviruses?

You can help prevent infection by doing the following:

  • Wash your hands before eating or preparing food. This is especially important if you have just changed any diapers or used the toilet.
  • Wash fruits and vegetables and steam oysters before eating them.
  • Clean and disinfect contaminated surfaces immediately after vomiting or having diarrhea by using a bleach-based household cleaner.
  • Immediately remove and wash soiled clothing or linens after vomiting or having diarrhea. Use hot water and soap.
  • Flush vomit and/or stool in the toilet, and make sure that the surrounding area is kept clean.
  • Do not prepare food if you have symptoms of food poisoning and for 3 days after you recover.

Last Updated: February 23, 2009

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