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What are noroviruses?

Noroviruses are a group of viruses, responsible for a condition known around the world as gastro-enteritis. Previously known as, Norwalk-like virus, and often labeled as the stomach flu, this group of viruses is highly infectious. There are 5 main sub-groups of noroviruses, but it is the GI, GII, or GIV subgroups that are involved in human illness. The noroviruses are part of a larger family of viruses called caliciviruses, which often infect animals.

As few as 100 virus particles are required to cause infection. People experience symptoms of the illness usually within 24 to 48 hours after being exposed. It is believed that 30% of infectious persons do not present symptoms.

 
How are noroviruses transmitted?

The virus is passed in the feces and vomit of an infected individual. The virus can be passed in the feces for up to 2 weeks after the symptoms disappear.

Food and drinks are often contaminated with the virus from unwashed hands of ill persons. Food can also be contaminated from sewage water used to rinse produce or used in the production of food. Surfaces contaminated by airborne droplets of vomit from an infected individual can also be a source of infection. The virus can survive on surfaces for up to 12 hours.  It can also survive freezing and temperatures up to 60^oC.

Direct contact with infected persons is the major mode of transmission. Outbreaks are common in situations where persons are in close quarters i.e. nursing homes, hospitals, and cruise ships.

What are the symptoms and duration of norovirus infections?

Symptoms last for 1 to 2 days and, as with most viral infections, there is no specific treatment available. The most common serious complication is dehydration, which may require intravenous fluid replacement in severe cases. Drinking plenty of water to replenish the body is recommended in all cases of diarrhea.

Common symptoms include:

• Vomiting 
• Watery, but not bloody, diarrhea
• Abdominal cramps
• Nausea
• Fever
• Headache
• General malaise
• Sore body. 

No immunity is developed to the noroviruses because the infective strain differs over time.

What precautions can you take?

1. Wash your hands often, especially before handling food. Current recommendations are for 20 seconds using soap and water. 

2. Wash your fruits and vegetables in potable water, especially if they are going to be consumed raw. 

3. Clean all surfaces that may have been sprayed by vomit and/or feces thoroughly. The virus is susceptible to a 1% bleach solution. 

4. Discard any food or drink that may have been contaminated.

Links:

Centers for Disease Control and Prevention. (2006). Norovirus: Food Handlers. Retrieved from, http://www.cdc.gov/ncidod/dvrd/revb/gastro/norovirus-foodhandlers.htm

Centers for Disease Control and Prevention. (2006).  Norovirus: Technical Fact sheet. Retrieved from,  http://www.cdc.gov/ncidod/dvrd/revb/gastro/norovirus-factsheet.htm

Public Health Agency of Canada. (2001). Material Safety Data Sheet – Norwalk virus. Retrieved from http://www.phac-aspc.gc.ca/msds-ftss/msds112e.html

Public Health Agency of Canada. (2005). Noroviruses – Fact sheet. Retrieved from http://phac-aspc.gc.ca/id-mi/norovirus-eng.php

Tu, E., Bull, R., Greening,G., Hewitt, J., Lyon, M., Marshal, J., et. al. (2008). Epidemics of Gastroenteritis during 2006 Were Associated with the Spread of Norovirus GII.4 Varients 2006a and 2006b. Clinical Infectious Disease. 46. 413-420.