MUNICIPAL DRINKING-WATER AND CRYPTOSPORIDIOSIS AMONG PERSONS WITH AIDS IN LOS-ANGELES-COUNTY

To assess unfiltered drinking water as a source of cryptosporidium inf ection in patients with the acquired immunodeficiency syndrome (AIDS) the prevalence of cryptosporidiosis among persons with AIDS in Los Ang eles County was assessed by mater service area. One water distributor, serving approximately 60% of the county's residents (area B), has con sistently employed filtration. The other company, which serves the rem ainder of the county (area A), did not institute filtration until mid- December 1986. This difference provided a 'natural experiment' in whic h to assess the effect of municipal water filtration on the level of c ryptosporidiosis among persons with AIDS. The prevalence of cryptospor idiosis among AIDS patients was compared for the two water service are as for the time period (1983-6) preceding the implementation of filtra tion in area A. From 1983 to 1986 the age-standardized prevalence of c ryptosporidiosis among AIDS patients was 32% lower in area A (4.2%), w hich received unfiltered water, than in area B (6.2%). Following addit ion of filtration in area A, the prevalence of cryptosporidiosis among AIDS patients decreased by 20%; however, a decline, of 47%, was also observed in area B. The similar baseline levels of cryptosporidiosis a nd the corresponding post-filtration decline in both areas suggest tha t filtration had no effect on levels of cryptosporidiosis among person s with AIDS. Thus it does not appear that municipal drinking water is an important risk factor for cryptosporidiosis in AIDS patients residi ng in Los Angeles County.