Norwalk virus family
virus is the prototype of a family of unclassified small round structured
disease is self-limiting, mild, and characterized by nausea, vomiting,
diarrhea, and abdominal pain. Headache and low-grade fever may occur.
few laboratories possessing reagents from human volunteer studies
can only make specific diagnosis of the disease.
of the virus can be made on early stool specimens using immune electron
microscopy and various immunoassays.
faecal-oral route via contaminated water and foods transmits Norwalk
person-to-person transmission also occurs. Water is the most common
source of outbreaks and may include water from municipal supplies,
well, recreational lakes, swimming pools, and water stored aboard
and salad ingredients are often implicated in Norwalk outbreaks.
Ingestion of raw or insufficiently steamed clams and oysters poses
a high risk for infection with Norwalk virus. Ill food handlers
contaminate foods other than shellfish
viral gastroenteritis is caused by a number of viruses, it is estimated
that Norwalk viruses are responsible for about 1/3 of the cases
not involving the 6-to-24-month age group. In developing countries
the percentage of individuals who have developed immunity is very
high at an early age. In the U.S. the percentage increases gradually
with age, reaching 50% in the population over 18 years of age.
is not permanent and reinfection can occur.
A mild and brief illness usually develops 24-48 h after contaminated
food or water is consumed and lasts for 24-60 hours. Severe illness
or hospitalization is very rare. All individuals who ingest the
virus and who have not (within 24 months) had an infection with
the same or related strain, are susceptible to infection. Disease
is more frequent in adults and older children than in the very young.