Noroviruses (Norwalk Viruses)

Condition Basics

What are noroviruses?

Noroviruses are also called Norwalk-like viruses and caliciviruses. Noroviruses cause gastroenteritis, food infection, food poisoning, and acute nonbacterial gastroenteritis.

What causes them?

Noroviruses typically spread through contaminated water and foods, although they can also pass from person to person. Water becomes contaminated if human waste enters drinking water because of flooding or from a sewage system that isn't working properly. 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.

Keep your child at home while they are sick and for a few days after feeling better. That's when the virus most likely can be spread to others. The virus can stay in your child's stool for weeks after the symptoms are gone.

What are the symptoms?

The symptoms of gastroenteritis caused by the noroviruses include nausea, vomiting, diarrhea, and abdominal (belly) pain. Diarrhea and vomiting can cause dehydration. You may have a headache and a fever. A mild and brief illness usually develops 24 to 48 hours after you eat or drink the contaminated food or water and lasts for 48 to 72 hours. Only in rare cases does a person get very sick or have to go to the hospital.

How are they diagnosed?

Most norovirus infections are mild and pass in a few days. So most people do not go to their doctors 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 doctor, they will make the diagnosis based on your symptoms, a medical history, and a physical exam. Your doctor 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 norovirus infections treated?

You treat gastroenteritis caused by noroviruses by managing 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 doctor recommends them.

To prevent dehydration, drink plenty of fluids. Choose water and other clear liquids until you feel better. You can take frequent sips of a rehydration drink (such as Pedialyte). Soda, fruit juices, and sports drinks have too much sugar and not enough of the important electrolytes that are lost during diarrhea. These kinds of drinks should not be used to rehydrate. In cases of severe dehydration, fluids may need to be replaced through an I.V. (intravenously).

When you feel like eating again, start with small amounts of food.

If you had diarrhea caused by norovirus, you should stay home for 2 to 3 days after your symptoms end before going back to work or school. This will help prevent spread of the virus.

How can you prevent them?

You can help prevent infection by doing the following:

• Use soap and water to wash your hands often. (Alcohol-based hand sanitizers do not kill noroviruses.) It is especially important to wash your hands after using the bathroom and before handling food.
• Wash fruits and vegetables and cook shellfish before eating them.
• If you suspect that your drinking water is contaminated, boil water for 1 minute (3 minutes at elevations above 5,000 feet). Then cool and refrigerate it. Water filters will not remove noroviruses.
• Clean and disinfect contaminated surfaces immediately after vomiting or having diarrhea by using a bleach-based household cleaner. To dilute household bleach, follow the directions on the label.
• Wear gloves to 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 2 to 3 days after you recover.