It is now well established that enteric viruses, such as hepatitis A, Norwalk, rotavirus, and so forth, can be transmitted by sewage-contaminated water and food. Standards for viruses in water have been suggested by the World Health Organization and several other organizations. Few attempts have been made to assess the risks associated with exposure to low numbers of enteric viruses in the environment.

To determine the risks that may be associated with exposure to human enteric viruses, the literature on minimum infectious dose, incidence of clinical illness, and mortality was reviewed. This information was then used to assess the probability of infection, illness, and mortality for individuals consuming drinking water containing various concentrations of enteric viruses. Risks were determined on a daily, annual, and lifetime basis. This analysis suggested that significant risks of illness (>1:10 000) and mortality (>1:1 000 000) may arise from the exposure to low levels of the enteric virus.