EPA was right on this Primary Pathogen in sludge Biosolids
12. Norwalk like viruses -------------------------- Gastroenteritis
Common names of the illness caused by noroviruses (previously called Norwalk-like viruses) are winter vomiting
disease, viral gastroenteritis, acute nonbacterial gastroenteritis, (incorrectly) food poisoning, and (most commonly in
American English) stomach flu. The virus can cause symptoms such as stomach pain, diarrhea, and vomiting in humans,
as well as general lethargy and weakness.
Norwalk gastroenteritis is transmitted by the fecal-oral route via contaminated water and foods. Secondary
person-to-person transmission has been documented. Water is the most common source of outbreaks and may include
water from municipal supplies, wells, recreational lakes, swimming pools, and ice machines.
Shellfish and salad ingredients are the foods most often implicated in Norwalk outbreaks. Ingestion of raw or
insufficiently steamed clams and oysters poses a high risk for infection with Norwalk virus. Foods other than shellfish are
contaminated by ill food handlers.
Norovirus continues to be a problem on cruise ships. In 2002, there were 25 reported outbreaks, with 2,648 passengers
becoming ill from the virus.  Outbreak investigations by the U. S. Centers for Disease Control and Prevention have
shown that transmission among cruise ship passengers is almost wholly person-to-person. Cruise ship water supplies
have never been implicated.
Only the common cold is reported more frequently than viral gastroenteritis as a cause of illness in the U.S. Although
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 at an early age is very high. In the U.S. the percentage increases gradually with age, reaching 50%
in the population over 18 years of age. Immunity, however, is not permanent and reinfection can occur. There is some
evidence that blood types B and AB confer partial protection against symptomatic infection.
Norovirus causes acute gastroenteritis that usually develops 24-48 h after contaminated food or water is consumed and
lasts for 24-60 hours. Severe illness is rare, although people are frequently treated in emergency rooms, they are rarely
admitted to the hospital. The number of deaths from norovirus in the US is estimated to be around 300, with most of
these occuring in the elderly.