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It has been reported that 95% of non-bacterial gastroenteritis outbreaks are attributable to human caliciviruses, which include Norwalk and Norwalk-like viruses (NV). Although Norwalk infections occur year round and are responsible for widely publicized outbreaks (on cruise ships, etc), they are more prevalent in winter. Sources of infection are highly variable & include contaminated drinking water, swimming pool water, ice cubes, or almost any food substance including cooked meat, salads, and fresh fruit. Undercooked contaminated shellfish is likely a major source of transmission. The initial infection generally results from a common contaminated source, with secondary infections resulting from person to person transmission. The incubation period of NV is generally 18 to 72 hours, with symptoms including malaise, myalgia, abdominal cramps, and low-grade fever. Vomiting is more common in children, while watery, nonbloody diarrhea is more common in adults. Symptoms may persist for 48 to 72 hours. Treatment is supportive, and aimed primarily at preventing dehydration, as no specific antiviral therapy is available.

Although NV is becoming more prevalent, neonates and very young children are more likely infected by rotavirus or adenovirus, particularly during the winter months. Rotavirus is transmitted primarily by the fecal-oral route, generally without an identifiable common source. Regional outbreaks usually persist for 4-5 months. Susceptibility to rotavirus is thought to be lifelong, with the most severe disease occurring during an infant’s primary infection. Adenovirus is another prominent pathogen in infantile diarrhea, and symptoms may persist for one to two weeks after infection.

None of these three prevalent causes of gastroenteritis can be recovered by routine viral cultures. Identification of a particular virus is often unnecessary, particularly in adult patients. Enzyme immunoassay tests are available for the diagnosis of rotavirus and adenovirus, and more recently for NV.

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