Giardia and Cryptosporidium infection risk by simultaneous exposure to drinking water

- Giardia and Cryptosporidium infection risk due to drinking water ingestion was elevated.
- Giardia was determinant for the results of the combined risk.
- DALY for adults by cryptosporidiosis was higher than WHO recommendation (10−6).

The fecal contamination of water sources represents a health risk for the population consuming drinking water from Water Treatment Plants (WTP) supplied by these sources. Giardia and Cryptosporidium protozoa pose major risks because they are excreted at high densities, survive for long periods in the environment and can remain infectious. Considering the relevance of both parasites in waterborne outbreaks, the objective of this study was to assess the probability of infection by both parasites in a population supplied by drinking water contaminated with Giardia cysts and Cryptosporidium oocysts using the Quantitative Microbial Risk Assessment (QMRA) approach. The model of dose-response used for estimating the risk for children and adults was the same but with a lower ingestion rate of water for children. Results showed that the annual risks of infection for adults and children exposed by direct consumption of drinking water and indirect consumption during bathing were higher than the tolerable annual risk of 1/10,000 issued by the US EPA. The risk of infection by Giardia was the major determinant for the combined risk. The results obtained in this study showed DALY values ranging from 5.2 × 10−6 to 6.5 × 10−6 ppy, elevated levels according to WHO recommendations. The QMRA approach is strategic for determining the acceptable level of treatment by WTPs and information on the efficiency of sanitary barriers.