Is contaminated groundwater an important cause of viral gastroenteritis? (Practical Stuff!).

* In a large number of the reported waterborne outbreaks, no etiological agent could be identified.

* It has been suggested that a significant fraction of these outbreaks may be caused by virus contamination of drinking water.

* The probability that viral outbreaks will be detected is low for groundwater systems.

* It is difficult to detect viruses either in infected humans or in drinking water near the time of an outbreak.

* There may be other reasons that waterborne virus outbreaks seem to be relatively uncommon:

-- Natural waters may inactivate the viruses.

-- The infectious dose for certain enteric viruses may be relatively high.

-- Disease-surveillance systems are relatively insensitive to increases in mild gastroenteritis.

* It is not known how many waterborne outbreaks go unrecognized and the extent to which viral outbreaks may be underestimated in the United States.

* Concerns about contamination of underground water supplies and human health risks have prompted a number of studies of virus occurrence in groundwater.

* The studies have in fact detected viruses in groundwater.

* Many of these studies selected high-risk or sewage-contaminated wells for testing, however.

* The results likely overestimated the occurrence of virus contamination in groundwater as well as the resulting public-health risks.

* Only limited evidence has been found for viral contamination of groundwater in the absence of bacterial indicators of sewage contamination.

* To better estimate the potential health risks, surveys should look at the occurrence of virus contamination in groundwater that does not have bacterial indicators of sewage contamination and in water that has not been adequately disinfected.

* These surveys should include groundwater from a wide range of geological conditions.