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 infection with noroviruses?

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.

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 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. Only in rare cases does a person get very sick or have to go to the hospital.

How are infections with noroviruses 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, he or she 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 infections with noroviruses 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, take frequent sips of a rehydration drink (such as Pedialyte). Try to drink a cup of water or rehydration drink for each large, loose stool you have. 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).