Canadian Institute of Public Health Inspectors


What is Norwalk Virus?

Norwalk virus is a very common source of non-bacterial diarrhea and vomiting in humans. Symptoms usually have a sudden onset and include watery diarrhea, vomiting, cramps, headache, fever, chills and sore throat. The illness usually last 24 to 48 hours.
There are several different viruses that make up the Norwalk and Norwalk-like viruses. The virus is very small and often difficult to detect.
Norwalk viruses are more commonly associated with outbreaks in nursing homes, homes for the aged and other adult institutions due to the close proximity of the residents. Outbreaks have also been linked to banquets, cruise ships, swimming pools, schools and restaurants. 

How is The Norwalk Virus Spread?

Man is the only known reservoir for the Norwalk virus. It is probably spread by the "fecal-oral" route,although direct contact or airborne transmission has been suggested to explain the rapid spread in institutions. The virus is very contagious and only a few are needed to cause illness.
Contaminated water is the most common source for outbreaks other than in institutions. Shellfish and salad ingredients are the foods most often implicated in Norwalk outbreaks.



Immunity against the virus is usually short-term, about 14 days. The incidence of illness can occur year round however, it is higher in the fall and winter.

How Do You Prevent Norwalk


. Thorough hand washing is the best prevention. Make sure hands are properly washed after using the toilet, changing diapers and preparing food.

. People ill with diarrhea and Norwalk like symptoms should be isolated from others.

. Dispose of feces and fecally contaminated material carefully.

. Clean and sanitize washrooms and all hand contact surfaces once daily or as needed.

. In institutions, isolate ill residents from group activities until they are symptom-free for 48 hours. Ill staff should remain off work until symptom-free for 48 hours.

. Encourage visitors to wash their hands before and after visiting the facility.