The illness usually runs its course in about 1-2 days. Acquired immunity is poor, lasting a year or so at best. Prevention Prevention requires a concerted effort to improve sanitation and hygiene standards within any community. Thus many outbreaks can be prevented by enforcing sanitation standards that apply to the preparation and supply of food for public consumption, for many epidemics start at the hands of an ill food handler. Interestingly, however, nearly half of all the Norwalk outbreaks investigated by the Center for Disease Control have been traced back to shellfish that was served raw or undercooked.
Shellfish are notorious for concentrating viruses in fecally contaminated waters.
Thorough cooking of food is a very good means of preventing viral transmission. Unfortunately, uncooked foods such as salads thus pose the greatest risk. Interestingly enough, caliciviruses are also relatively resistant to chlorination of water. An Update Recently molecular techniques have developed for detection and diagnosis of enteric viruses in water samples. This has proved to be a boon to Public Health officials who are concerned about the transmission of Norwalk through shellfish consumption and contaminated water resources.