Causes and Symptoms of Norovirus Infection

Noroviruses are members of a group of viruses called caliciviruses, known previously as “Norwalk-like viruses.” This infection is often mistakenly referred to as the “stomach flu,” but noroviruses are not related to the flu (influenza), which is a respiratory illness caused by influenza virus. Norovirus is also sometimes called viral gastroenteritis, food poisoning, and calicivirus.

Norovirus infection causes gastroenteritis, which is an inflammation of the stomach and the small and large intestines. Norovirus is by far the leading cause of foodborne illness outbreaks in Minnesota and the rest of the U.S.

Norovirus is not a “new” virus, but interest in it is growing as more is learned about how frequently noroviruses cause illness in people.

Fact Sheet

• Norovirus Fact Sheet (PDF)
  MDH fact sheet that answers common questions about norovirus.
  • Spanish (PDF)

Symptoms

Common symptoms include:

• nausea
• vomiting
• diarrhea
• abdominal cramps

Other symptoms may include:

• headache
• fever/chills
• muscle aches

Symptoms usually last 1 or 2 days. However, during that brief period, people can feel very ill and vomit, often violently and without warning, many times a day.

Duration of Illness

• Symptoms usually begin 24 to 48 hours after ingestion of the virus, but can appear as early as 12 hours after exposure.
• There is no evidence that sick persons can become long-term carriers of the virus, but the virus can be in the stool and vomit of infected persons, from the day they start to feel ill to as long as 2 weeks after they feel better.
   

Transmission

• Noroviruses are found in the stool or vomit of infected people. People can become infected with the virus in several ways, including:
  • eating food or drinking liquids that are contaminated with norovirus by foodhandlers who have not washed their hands adequately
  • touching surfaces or objects contaminated with norovirus, and then placing their hand in their mouth or eating before washing their hands
  • having direct contact with another person who is infected and showing symptoms (for example, when caring for someone with illness, or sharing foods or eating utensils with someone who is ill)
  • swimming in or drinking water contaminated by infected persons
• Persons working in day-care centers or nursing homes should pay special attention to children or residents who have norovirus illness. This virus is very contagious and can spread rapidly throughout such environments.

Do you suspect that you have a foodborne or waterborne illness? Visit reporting suspected foodborne/waterborne illnesses.