Health risks and parasitical quality of water

Abstract

This article assesses the risks of acute digestive conditions (ADC) in relation to protozoa Giardia and Cryptosporidium conveyed through drinking water within a French general population. It is a part of the Epidemiology and Microbial Risk Assessment study, which combined a daily epidemiological followup among a panel of volunteers whose water was supplied by vulnerable public water systems. These systems were monitored with a microbiological surveillance of the tap water. Parasitical quality of the water was assessed using cartridge and immunofluorescence assays. The relationship between incidence of ADC and waterborne protozoa was modeled using logistic regression and generalized estimating equations analysis. During the study period, 712 cases of ADC occurred. Thirty‐six tap water samples were collected for parasitical quality analysis. of these, 11 tested positive for at least one protozoan, among which 10 complied with bacterial criteria. The final model included concentrations of Giardia cysts and several confounding factors; unfortunately, Cryptosporidium data were too sparse for analysis. Biostatistical modeling showed that Giardia detection was associated with an increased risk of ADC: relative risk (RR) = 1.19 (95% confidence interval = [0.96–1.48]) for 10 to 20 cysts/100 L, and RR = 1.24 [1.06–1.45] for more than 20 cysts/100 L, compared with absence of detectable cysts. These results suggest the role of Giardia in the endemic level of waterborne infectious diseases and raise the question of protozoa surveillance in drinking water, while traditional bacterial surveillance indicators have been shown to be poor predictors of their presence.