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Noroviruses are generally believed to cause relatively mild gastroenteritis of short duration in otherwise healthy adults. However, outbreaks in health care settings are common and affect vulnerable populations. During 2002-2003, a total of 4 major hospitals, 11 community hospitals, and 135 nursing homes in the county of Avon, England, were prospectively monitored for outbreaks of gastroenteritis. For 482 hospital staff, 166 nursing home staff, and 266 nursing home residents, the median duration of norovirus gastroenteritis was 2 days, with 75% achieving complete recovery within 3 days. The median duration of norovirus gastroenteritis for 730 hospital patients was 3 days (75% of the patients achieved complete recovery within 5 days), which was significantly longer than that for all other groups (P<.001). Therefore, infection in hospitalized persons may be more severe than that in other groups in the community at large. This increased duration of acute illness should be considered when implementing measures to prevent transmission in hospital settings.

In the period 1992–2000, the Public Health Laboratory Service Communicable Disease Surveillance Centre collected standardized epidemiologic data on 1,877 general outbreaks of Norovirus (formerly “Norwalk-like virus”) infection in England and Wales. Seventy-nine percent of general outbreaks occurred in health-care institutions, i.e., hospitals (40%) and residential-care facilities (39%). When compared with outbreaks in other settings, those in health-care institutions were unique in exhibiting a winter peak (p<0.0001); these outbreaks were also associated with significantly higher death rates and prolonged duration but were smaller in size and less likely to be foodborne. These data suggest that Norovirus infection has considerable impact on the health service and the vulnerable populations residing in institutions such as hospitals and residential homes. A distinct outbreak pattern in health-care institutions suggests a combination of host, virologic, and environmental factors that mediate these divergent epidemiologic patterns.

To gain understanding of surveillance and epidemiology of viral gastroenteritis outbreaks in Europe, we compiled data from 10 surveillance systems in the Foodborne Viruses in Europe network. Established surveillance systems found Norovirus to be responsible for >85% (N=3,714) of all nonbacterial outbreaks of gastroenteritis reported from 1995 to 2000. However, the absolute number and population-based rates of viral gastroenteritis outbreaks differed markedly among European surveillance systems. A wide range of estimates of the importance of foodborne transmission were also found. We review these differences within the context of the sources of outbreak surveillance information, clinical definitions, and structures of the outbreak surveillance systems.