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Norwalk Virus

What is Norwalk virus?

Norwalk is a virus that commonly causes vomiting and diarrhea in people of all ages. Illness usually begins within 24 to 48 hours after infection. Symptoms have a sudden onset and include watery diarrhea, nausea, vomiting, cramps, headache and occasionally fever. Illness usually lasts 24 to 48 hours. Immunity against the virus is short-term, lasting up to 14 weeks.

Norwalk virus is frequently associated with outbreaks in nursing homes, retirement homes, daycare centres and schools due to the close proximity of the residents. Even though most cases are included as part of an outbreak, single cases can occur. Infection is possible year round with case numbers being highest in the fall and winter.

Children and the elderly are at increased risk of suffering from dehydration as a result of infection. Consult a physician if you suspect dehydration.

How can you get sick from Norwalk virus?

• Humans are the only known reservoirs for the Norwalk virus. Norwalk is probably spread through hand to mouth contact following contamination of the hands with the feces of an infected individual. Contact with contaminated surfaces may also lead to infection.
• Transmission through the air is another possible way of becoming infected. This is due to the airborne spray of the virus during vomiting. The virus is very contagious, and only a few particles are needed to cause illness.
• Contaminated water is the most common source of Norwalk virus outbreaks outside of institutions.
• Shellfish and salad ingredients are the foods most often implicated in Norwalk outbreaks.

How do you prevent Norwalk virus infections?

1. Thorough handwashing is the best prevention. Make sure that you properly wash your hands after using the toilet and changing diapers. Always wash your hands before and after handling food.
2. Individuals ill with Norwalk-like symptoms should not handle food.
3. Ensure that feces and fecally contaminated material are carefully disposed of and disinfect all contaminated surfaces.
4. Clean and sanitize washrooms and all hand contact surfaces with a solution of 1 part bleach to 9 parts water (i.e. 1 oz. bleach in 9 oz. water) once daily or as needed.
5. If you are not on a municipal drinking water system, make sure that your water is safe by conducting regular sampling.
6. Thoroughly cook shellfish prior to eating
7. Wash all fruits and vegetables thoroughly before consumption

What steps should be taken to clean and disinfect a school facility?

See cleaning and disinfecting for schools.

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