Norwalk virus is a virulent flu-like virus that causes intense intestinal illness (gastroenteritis). It is not influenza, however.
The virus was first identified in 1972 after an outbreak of gastrointestinal illness at a school in Norwalk, Ohio. This virus and its variants have been classified as members of the calicivirus family.
At time of noding (Dec. 2002) this virus has been making news due to outbreaks on cruise ships, schools, office buildings, and hospitals. It is highly communicable and tends to quickly spread through communities with shared restroom facilities.
Symptoms
Symptoms of Norwalk usually appear one or two days after infection. Symptoms vary between individuals, but can include:
Severe dehydration often results from a combination of the above symptoms.
Transmission and Prevention
In doctor-speak, the Norwalk gastroenteritis is primarily transmitted by the "fecal-oral route" -- in other words, through the stool of infected persons. Not directly, of course, but indirectly through contaminated water and food. Water is the most common source of outbreaks - vectors include drinking, bathing, swimming, and presence in shellfish and salad ingredients.
There is some suspicion that secondary person-to-person transmission through air or physical contact is possible.
It is also transmittable by fomites, commonly among children at school. Humans are the only known hosts.
Those planning on taking a cruise, take note: cruise ships seem to have been passing it to each other in port, where one ship dumps its sewage and another takes on water from the same source, and improperly or inadequately filters it. Eww.
Transmission usually occurs in the early stages of infection, before symptoms appear, making it all the more likely to spread rapidly in an infected area.
Norwalk is destroyed by thorough cooking of foods. It is not destroyed by freezing. To avoid it during an outbreak, make sure the food you eat is completely cooked. Drink pasteurized milk or bottled beverages without ice. Thoroughly wash, or preferably thoroughly cook, all food items; especially shellfish. Always wash your hands thoroughly with soap and warm water after using the toilet and before preparing or eating any food.
Enforcing rigorous attention to hand washing among all family members is the best defense.
Detection, treatment, and recovery
At time of noding, no diagnostic test is currently available for Norwalk. Diagnosis is often based on the combination of symptoms and the short time of illness.
During the November-December 2002 outbreak in Toronto, patients admitted to Emergency rooms across
the city were treated with an intravenous drip to rehydrate them (mixed with Gravol to control the nausea)
before being sent home.
Victims of the virus usually recover in 2 to 3 days without any long-term health effects.
Sources:
- http://www.astdhpphe.org/infect/norwalk.html
- http://vm.cfsan.fda.gov/~mow/chap34.html
- Local news reports
- Two nights hanging around in the Toronto Western Hospital emerg. unit.
See also Winter vomiting disease.