A PROSPECTIVE EPIDEMIOLOGIC-STUDY OF DRINKING-WATER RELATED GASTROINTESTINAL ILLNESSES

A prospective epidemiological study was undertaken to evaluate whether drinking water satisfying current quality standards nevertheless causes gastrointestinal illness. The study consisted of an health surveillance of 600 randomly chosen households (2400 individuals) and of the microbiological analysis of tap water from the filtration plant and its distribution system. Half of the households were randomly assigned to the tap water subgroup and half to a control subgroup. A reverse-osmosis filter was installed in each control household, thereby ensuring a very low microbiological pollution level. Each member of each household reported gastrointestinal symptoms on a bimonthly health calendar during two periods: March to June 1988 and September 1988 to June 1989. The incidence of highly credible gastrointestinal symptoms (HCGI) was markedly different in the two groups. During the first period the incidence of episodes/year was 0.82 in the group consuming filtered water and 1.13 amongst those consuming tap water. During the second period these values were respectively 0.47 (filter) and 0.62 (tap water). Differential incidence rates of HCGII between the two groups were observed in all age and sex groups. While tap water met acceptable standards of quality our results indicate that there was a 25% excess of gastrointestinal illness in the group consuming that water. Further analysis of the water quality and of the integrity of the distribution system are underway. Serum samples obtained at different phases of the study are also being analyzed to evaluate the incidence of viral enteric diseases in this population.