Because the infective dose (the number of organisms needed to cause disease) is very low in Norovirus infection, the disease is easily spread person-to-person. The virus is present in the feces and vomitus of an infected person, and transmission occurs primarily through the spread of the virus on hands, toys, bathroom surfaces and contaminated food, etc. There is some evidence that Norovirus may also be transmitted via aerosolized vomitus to persons caring for, or cleaning up after acutely ill persons. Infected persons may remain infectious for up to one month after onset of symptoms. There are many different strains of norovirus, so people can develop illness repeatedly when exposed to different strains of the virus. Treatment typically consists of supportive care, primarily fluid and electrolyte replacement.

Laboratory testing for noroviruses is not routinely performed and is not available at most commercial laboratories. For epidemiologic purposes, such as confirming the cause of large outbreaks, testing of feces and vomitus for noroviruses by reverse transcriptase polymerase chain reaction (RT-PCR) is available at the Washington State Department of Health Laboratory with prior approval through Public Health-Seattle & King County.

Good hygiene, especially hand washing after using the bathroom, after changing diapers, and before preparing food is the best way to prevent the spread of noroviruses and other types of AGE of infectious etiology. Other methods of prevention include:

1. Thoroughly cleaning surfaces contaminated by feces or vomitus immediately, and disinfecting with a 10% bleach and water solution.
2. Immediately removing contaminated clothing or linens after an episode of illness and washing with hot water and soap.
3. Discarding any vomitus or stool in the toilet and making sure that the surrounding area is kept clean.
4. Excluding foodhandlers and healthcare workers with symptoms of acute gastroenteritis from work for at least one day following cessation of the acute symptoms.

There have been a number of outbreaks of norovirus infection in the past year, both locally and nationally. Recent laboratory-confirmed outbreaks in King County have occurred at nursing homes, daycare centers and among hospital staff. For more information about testing specimens for noroviruses in the setting of an outbreak, contact Public Health-Seattle & King County at 206-296-4774. For summary articles on recent outbreaks nationwide, and general information on norovirus infection, go to:

www.cdc.gov/mmwr/preview/mmwrhtml/mm5203a1.htm
www.cdc.gov/mmwr/preview/mmwrhtml/mm5149a2.htm
www.cdc.gov/ncidod/dvrd/revb/gastro/norovirus.htm

Article reprinted with permission from Public Health-Seattle & King County's EPI-LOG Newsletter, Feb. 2003.

Laurie Stewart, M.S., is Epidemiology Surveillance Coordinator in the Communicable Disease Epidemiology and Immunization department of Public Health-Seattle & King County. She can be reached at laurie.stewart@metrokc.gov. Public Health-Seattle & King County's Web site is www.metrokc.gov/health.