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Noroviruses by Rebecca J. Stahl, MA

Definition

Noroviruses refer to a group of viruses. They cause inflammation of the stomach and intestines. It is called gastroenteritis or the stomach flu. In the US, they are the second leading cause of illness. Outbreaks have occurred in settings such as:

Cruise ships
Restaurants
Nursing homes
Hospitals
Any other location where the virus can spread quickly to a large group of people

The Digestive Tract

Causes

These viruses are highly contagious. They are spread by fecal to oral contamination of water and food.

Infection can occur as a result of contaminated:

Municipal water supplies, recreational lakes, swimming pools, wells, water stored on cruise ships, among other sources
Raw (or improperly steamed) shellfish, especially clams and oysters
Food and drinks (due to infected food handlers who either do not wash their hands or wash their hands improperly after using the bathroom)
Surfaces (eg, touching a door knob and then placing hands in mouth)

The viruses can also spread by direct contact with an ill person. This is common in a daycare center or nursing home.

Risk Factors

The following factors increase your chance of developing noroviruses:

Age: more common in adults and children than the very young
Being exposed to a contaminated water supply (eg, recreational lake)
Consuming contaminated foods or liquids
Touching contaminated surfaces
Taking care of someone who is infected with the virus (eg, in a nursing home or daycare center)
- Note: A person is contagious from the start of symptoms to at least three days after recovery. Sometimes it can be up to three weeks.

Even if you have been infected with norovirus in the past, you can become ill again if:

It is a different strain
It is over 24 months since your last exposure

Symptoms

If you have any of these do not assume it is due to norovirus. These may be caused by other, less serious health conditions. If you have any one these symptoms, see your doctor:

Nausea
Vomiting
- An infected person may vomit often (sometimes violently and without warning) during one day.
Diarrhea
Abdominal pain
Headache
Low-grade fever
Chills
Muscle aches
Tiredness
Dehydration
- This may require medical attention, especially in children, the elderly, and those with compromised immune systems
- Prevent dehydration by drinking a lot of fluids, including water and juice

After exposure to the virus, symptoms often appear within 24-48 hours. You may feel ill as early as 12 hours. Symptoms often last about 24-60 hours.

Diagnosis

Your doctor will ask about your symptoms and medical history. A physical exam will be done.

Diagnosis can be made based on a stool specimen. Often, your doctor can determine this illness without ordering any lab tests.

Treatment

Currently, there are no treatments. Because gastroenteritis is caused by a virus, antibiotics cannot cure it. There are no antiviral medications or vaccines. The illness is often brief.

The only complication would be dehydration due to vomiting and diarrhea. In certain groups of people, this may require a hospital stay to replenish fluids.

Prevention

Noroviruses can survive extreme heat and cold. The virus can also live in water with up to 10 parts per million of chlorine. This is much higher than what public water supplies have. There are ways, though, to limit exposure.

To help reduce your chance of getting noroviruses take the following steps:

Wash your hands thoroughly after using the bathroom (or changing diapers). This is very important before handling food or eating. If you are caring for someone who is infected, make sure the person thoroughly washes his or her hands.
Wash fruits and vegetables. Steam oysters and clams.
Do not prepare food if you have symptoms. Wait three days after you have recovered before handling food again.
Throw away contaminated food.
If you are ill or caring for someone who is ill, immediately clean and disinfect contaminated surfaces using bleach cleaner. Remove and wash soiled linens. Use hot water and soap.
If you are sick, do not attend work. Staying home will prevent you from passing the virus to others.
If you work in a healthcare facility, isolate sick individuals to reduce the virus from spreading.

RESOURCES:

National Institute of Allergies and Infectious Diseases http://www3.niaid.nih.gov/
US Centers for Disease Control and Prevention http://www.cdc.gov/
US Food and Drug Administration http://www.fda.gov/

CANADIAN RESOURCES:

BC Health Guide http://www.bchealthguide.org/
Communicable Disease Control Unit http://www.gov.mb.ca/health/publichealth/cdc/index.html
Health Canada http://www.hc-sc.gc.ca/index_e.html

References:

Causes and symptoms of norovirus infection. Minnesota Department of Health website. Available at: http://www.health.state.mn.us/divs/idepc/diseases/norovirus/basics.html . Accessed June 11, 2007.
Foodborne diseases: norovirus infection. National Institute of Allergies and Infectious Diseases website. Available at: http://www3.niaid.nih.gov/healthscience/healthtopics/norovirus/diagnosis.htm . Accessed June 12, 2007.
Norovirus: food handlers. National Center for Infectious Diseases: Respiratory and Enteric Viruses Branch. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/ncidod/dvrd/revb/gastro/norovirus-foodhandlers.htm . Accessed June 11, 2007.
Norovirus in healthcare facilities fact sheet. National Center for Infectious Diseases: Respiratory and Enteric Viruses Branch. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/ncidod/dhqp/id_norovirusFS.html . Accessed June 11, 2007.
Norovirus: Q&A. National Center for Infectious Diseases: Respiratory and Enteric Viruses Branch. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/ncidod/dvrd/revb/gastro/norovirus-qa.htm . Accessed June 11, 2007.
Norovirus: technical fact sheet. National Center for Infectious Diseases: Respiratory and Enteric Viruses Branch. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/ncidod/dvrd/revb/gastro/norovirus-factsheet.htm . Accessed June 11, 2007.
The Norwalk virus family. In: The Bad Bug Book: Foodborne Pathogenic Microorganisms and Natural Toxins Handbook . US Food and Drug Administration; 1992. Center for Food Safety and Applied Nutrition website. Available at: http://www.cfsan.fda.gov/~mow/chap34.html . Accessed June 11, 2007.
Preventing norovirus. Minnesota Department of Health website. Available at: http://www.health.state.mn.us/divs/idepc/diseases/norovirus/prevention.html . Accessed June 11, 2007.

Last reviewed January 2010 by David L. Horn, MD, FACP

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