Norovirus Infection - Epidemiology

What is norovirus infection?

Norovirus infection is caused by a very contagious virus called norovirus. The infection is characterized by sudden onset of nausea, vomiting, diarrhea, and stomach cramping. Although norovirus infection is sometimes called the “stomach flu,” norovirus is not related to the influenza (flu) virus that causes respiratory illness.

Who gets norovirus infection?

Anyone can get sick from norovirus. Because there are many different strains of norovirus, people who have been sick with norovirus can get it more than once. Outbreaks caused by norovirus occur in a variety of places, including healthcare settings (e.g., long-term care facilities, hospitals), restaurants, schools, day care centers, and cruise ships.

How is norovirus spread?

The virus is found in the stool and vomit of infected people and can spread easily from person to person. People infected with norovirus are most contagious from the time they first start feeling ill through three days after they feel well again. People sometimes remain contagious for up to a month after they have recovered. People can become infected by eating food or drinking liquids that are contaminated by infected food handlers, touching surfaces or objects contaminated with norovirus and then touching their mouth before hand washing, or having direct contact with another person who is infected and then touching their mouth before hand washing. Therefore, good hand washing is the key to preventing the spread of norovirus.

What are the symptoms of norovirus infection?

Symptoms usually include nausea, vomiting, diarrhea, and abdominal pain. Sometimes people have a low-grade fever, chills, headache, muscle aches, and a general sense of tiredness. Dehydration is the most common complication of illness.

How soon after exposure do symptoms appear?

Symptoms of norovirus infection usually begin 10–50 hours after exposure. The illness is usually brief, with symptoms lasting 1–3 days.

How is norovirus infection diagnosed?

Norovirus infection is usually diagnosed based on the symptoms a person is experiencing. During outbreaks, public health laboratories can test stool specimens to identify the virus and confirm the cause of the outbreak.

What is the treatment for norovirus infection?

There is no specific medication or vaccine for norovirus infection, and it cannot be treated with antibiotics. Drinking plenty of liquids, such as water or juice, is important to replace fluids lost from vomiting and diarrhea and prevent dehydration. Mild dehydration can be treated with oral fluids obtained from a pharmacy. People who become severely dehydrated should seek medical care.

How can norovirus infection be prevented?

Norovirus infection can be prevented in a number of ways, including:

Washing hands thoroughly with soap and water for at least 20 seconds, especially after using the restroom, changing diapers, sneezing, coughing, and before and after preparing food.
Staying home from work, school, or other activities when you are sick.
Cleaning and disinfecting contaminated surfaces with a bleach-based household cleaner immediately after vomiting or diarrheal accidents.
Washing clothing and linens if they become soiled.
Avoiding food preparation or caring for others while sick and for at least two days after symptoms stop.
Washing fruits and vegetables thoroughly before eating.
Avoiding food or water from sources that might be contaminated.
Cooking oysters and shellfish completely (to at least 140°F) before eating.

How long can an infected person carry norovirus?

People infected with norovirus can shed the virus in their feces (stool), even if they do not have symptoms. People are most contagious while they are ill and during the first few days after they recover. Most people can remain contagious for two weeks or more after they recover.

Should a person who has norovirus infection be excluded from work or school?

Yes. People should stay home when sick and for at least two days after symptoms stop to prevent spreading norovirus to other people.

How can I get more information about norovirus infection?

If you have concerns about norovirus infection, contact your healthcare provider.
Call your local health department. A directory of local health departments is located at the VDH Local Health Districts page.
Visit the Centers for Disease Control and Prevention website at the CDC's page on norovirus.