OUTBREAKS OF FOOD-BORNE AND WATERBORNE VIRAL GASTROENTERITIS

Norwalk virus was first identified in 1972 and subsequently shown to be a frequent cause of outbreaks of food-borne and waterborne viral gastroenteritis in the United States. From 1978 through 1982, the clinical and epidemiologic features of outbreaks of food-borne and waterborne Norwalk virus were characterized. These include the increased frequency of vomiting in relation to the frequency of fever, a median incubation period of 24 to 48 h, and a median duration of illness of 12 to 60 h. Norwalk virus infection is the epidemiologic prototype for outbreaks of food-borne and waterborne gastroenteritis caused by antigenically distinct viruses with similar morphology as visualized by electron microscopy. Laboratory confirmation has been limited by the poor sensitivity of electron microscopy and other methods for detecting virus particles in stool, our inability to isolate these viruses in cell culture, and restriction of the use of antibody detection assays to a few reference centers. Confirmed outbreaks of food-borne and waterborne Norwalk virus and Norwalk-like virus gastroenteritis have resulted from contamination of cold food items and ice by food handlers, consumption of raw shellfish, contamination of groundwater supplies, and swimming. In addition, person-to-person transmission of Norwalk virus infection among food handlers can perpetuate outbreaks, regardless of the primary source of the outbreak. National surveillance data on food-borne and waterborne illness in the United States and elsewhere underestimate the public health significance of viral gastroenteritis. In the absence of specific laboratory confirmation, epidemiologic classification of these outbreaks may provide a more accurate assessment of their public health significance.