Overview of Norovirus (Norwalk Virus) Infection

Cruises Got Your Cruising to the Bathroom?

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Cruiseships have a bad reputation for being the source of a diarrheal disease caused by a family of viruses called Norwalk viruses (also called norovirus, Norwalk-like virus, caliciviruses, and small round structured virus [SRSV]).

The infection has led to outbreaks at popular restaurants and fast food locales. It has also led to infections in nursing homes and hospitals.

Sometimes referred to colloquially as “stomach flu” (despite not having anything to do with the influenza virus), noroviruses are one of the viruses responsible for causing a diarrheal disease called viral gastroenteritis.

Did you know? Noroviruses (Norwalk viruses) were originally named for a town in Ohio, where a school outbreak provided the first viral strain to be characterized.

Type of Microbe: RNA virus

How it spreads: Norovirus is spread via the fecal-oral route through contaminated foods and water. Outbreaks are usually caused by contaminated water, such as stored water on cruise ships, swimming pools, and lakes. Foodborne infection may also occur when you consume norovirus-contaminated shellfish (such as clams and oysters) or foods prepared by cooks who are infected. Food handlers may carry the infection on their hands, returning to work with diarrhea or after a case of diarrhea.

Who’s at risk? All people are at risk for infection, but the disease is more common in adults and older children. Norovirus infections occur year-round, but are more common in the winter. A small number of people may have a gene that keeps them safe.

For everyone else, immunity may not last very long after an infection. Unlike many viruses, most are vulnerable again to another bout.

Symptoms: Approximately 24 to 48 hours after consuming contaminated food or water, symptoms appear and include nausea, vomiting, diarrhea, and abdominal pain. Symptoms may sometimes include headache or mild fever, as well.

The symptoms last for 24 to 72 hours.

Diagnosis: This disease cannot usually be distinguished from those caused by other bacteria or viruses. A diagnosis may be made when there is an outbreak or no other other causes. In these circumstances, microscopic examination of stool specimens (with electron microscopy) or laboratory tests can be used to detect the virus. Blood may be drawn for detection of antibodies made in response to the virus, but given the short-lived nature of disease, these kinds of laboratory tests are usually used for research purposes.

Prognosis: The disease is usually mild and self-limited. Severe disease or hospitalization are rare.

Treatment: There are no medications or vaccines for noroviruses. Treatment includes drinking plenty of fluids to avoid dehydration. Oral rehydration therapy may be used in severe cases of dehydration. Ask your doctor if he thinks it is necessary.

Prevention: Spread of norovirus can be limited by frequent hand-ashing, hygienic cooking and dining practices, and thorough cleaning or disinfection of surfaces and items that may be contaminated from others in your household. People who have been infected with norovirus may continue to shed the virus for up to 2 weeks after symptoms subside.

So they shouldn't prepare food.

How it causes disease: Norovirus has been difficult to study in laboratories, because there are currently no good systems for growing the virus outside of the human body. Therefore, little is known about how norovirus causes disease. There is some evidence that the virus grows in the small intestines of infected people, but why it causes symptoms of gastroenteritis is unclear.

Only a very tiny amount of infection is needed to spread the virus. Some people, who have a FUT2 mutation, are seemingly immune.

Immune response: People who get infected with norovirus develop short-term immunity that may last up to 24 months.

However, reinfection with norovirus can occur because the immunity against the virus is not permanent. A study showed that norovirus may evolve similarly to the flu virus.

Complications: Some people may be at risk for dehydration because of loss of fluids from vomiting and diarrhea. Dehydration is more common in the young, elderly, and people with weakened immune systems.


Lindesmith LC, et al. Mechanisms of GII.4 norovirus persistence in human populations. PLoS Medicine. 2004; 5: e31.

Lopman B, et al. The Evolution of Norovirus, the ”Gastric Flu”. PLOS Medicine. 2008; 5:187.

Norovirus: Q&A. National Center for Immunization and Respiratory Diseases. Division of Viral Diseases. CDC.

The Norwalk Virus Family. USFDA Bad Bug Book. Center for Food Safety and Nutrition.

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