Viral agents of gastroenteritis: public health importance and outbreak management

Morbidity and Mortality Weekly Report, April 27, 1991

The Norwalk agent can remain infective even if frozen for years or heated to 60 C for 30 minutes (80); however, cooking temperatures at boiling or above are probably adequate to inactivate Norwalk and most other enteric viral pathogens. Water

Outbreaks of viral gastroenteritis have been associated with various sources of contaminated water, including municipal water, well water, stream water, commercial ice, lake water, and pool water.

The most recent U. S. Environmental Protection Agency guidelines (June 29,1989) for municipal water systems recommend residual chlorine concentrations of -O.2 milligrams/liter (mg/L) (81), and in many localities peak levels of 5 mg/L are administered. Studies have documented that the Norwalk agent can remain highly infective despite 30-minute exposure to concentrations of chlorine as high as 6.25 mg/L, and levels of 10 mg/L appear necessary to inactivate it (82). This resistance may explain why the Norwalk agents are prominent in outbreaks of waterborne disease. Of 96 waterborne outbreaks with sufficient data reported to CDC from 1976 to 1979, 23% met epidemiologic criteria of a Norwalk virus outbreak (83), and subsequent surveillance data on waterborne outbreaks have been consistent with this finding. Of 38 serologically confirmed Norwalk virus outbreaks between 1976 and 1980, 13 were waterborne (52). Rotavirus, for which only one waterborne outbreak has been documented in the United States, is more sensitive to chlorine than the Norwalk agent and is inactivated by a 30-minute exposure to 3.75 mg/L (82). All viral agents of gastroenteritis are thought to be inactivated by boiling for 10 minutes.

Surfaces

Because rotavirus can survive for several days on nonporous materials in conditions of low temperature and humidity, fomites may contribute to its nosocomial transmission (84 ). A recent study of a Norwalk viral outbreak on a cruise ship implicated toilets shared between staterooms as a risk factor for infection, suggesting that surfaces contaminated by Norwalk particles from spattered or aerosolized material may play a role in transmission of Norwalk-like viruses (85). Data are lacking on the efficacy of disinfectants against Norwalk-like agents, but a number of germicidal chemicals have been shown in laboratory tests to be ineffective in reducing rotavirus activity (86-88). However, detergents do inactivate rotavirus (89) and should be used for laundering fecally contaminated linens and clothing. Thorough cleaning of environmental surfaces is required, as a minimum, to control spread of the viral agents of gastroenteritis.

Hands

Hands that have been contaminated directly or from surfaces may be the most important means by which enteric viruses are transmitted. Because the active ingredients in some commercial handwashing preparations are ineffective against rotavirus (90), the use of special handwashing products is not indicated. Vigorous handwashing with soap, performed consistently at appropriate intervals, is necessary to control the spread of all enteric pathogens. Aerosols