What is a Norovirus?

Norovirus is a very common virus that causes diarrhea and vomiting in humans. Noroviruses are named after the original Norwalk virus and Norwalk-like viruses. The viruses are very small and often difficult to detect. Noroviruses are commonly responsible for outbreaks in places where people are in close proximity to each other. Such places include nursing homes, homes for the aged, banquets, cruise ships, swimming pools, childcare centers, schools and restaurants.


Symptoms usually have a sudden onset and include:

  • watery non-bloody diarrhea
  • vomiting
  • abdominal cramps
  • nausea
  • Low-grade fever may occur and dehydration is possible.

The illness usually lasts 24 to 48 hours; however, Norovirus can still be spread for at least 48 hours after the symptoms stop.

How is it spread?

Humans are the only known reservoir for the Norovirus. Noroviruses are transmitted person to person and can also be transmitted through food. The “fecal-oral” route is the primary mode of transmission, although environmental contamination and aerosolization of the virus help explain the rapid spread in a group setting. Noroviruses are very contagious and only a few are needed to cause illness.

When is it contagious?

People infected with Norovirus are contagious from the moment they begin feeling ill to at least three days after recovery. Some people may be contagious for as long as two weeks after recovery. Good hygiene standards, including frequent hand washing or using hand sanitizer, are very important during this period.


Preventing infection

  • Proper hand hygiene is the best prevention. Make sure hands are properly washed after using the toilet, changing diapers and before preparing food.
  • People ill with diarrhea and other Norovirus symptoms should be isolated from others.
  • Carefully dispose of feces, and any materials contaminated with feces and/or vomitus.
  • Clean and sanitize washrooms and all hand contact surfaces once daily or as often as needed.
  • In long-term care institutions, isolate ill residents from group activities until they are symptom-free for at least 72 hours. Ill staff should remain off work until symptom-free for at least 72 hours.
  • Encourage visitors to long-term care institutions to wash their hands and/or use hand sanitizer before and after visiting the resident.


There is no preventative treatment (no vaccine or antiviral medication) for Noroviruses and they cannot be treated with antibiotics because antibiotics fight bacteria, not viruses. However, healthy people normally recover within one or two days, with symptoms resolving on their own.

Those suffering from illness should drink plenty of fluids to prevent dehydration – a possible serious health effect of Norovirus infection.

Young children, the elderly and people with other illnesses are at greatest risk for dehydration. Symptoms of dehydration in adults and children include a decrease in urination, a dry mouth and throat and dizziness upon standing. A dehydrated child may cry with few or no tears and be unusually sleepy or fussy. Severe dehydration can be serious and the ill person may require re-hydration in a hospital. If you think you or someone under your care is dehydrated, contact your healthcare provider.


Adapted from the Canadian Institute of Public Health Inspectors  (CIPHI) Fact Sheets.