The burden of drinking water-associated cryptosporidiosis in China: the large contribution of the immunodeficient population identified by quantitative microbial risk assessment.

A comprehensive quantitative microbial risk assessment (QMRA) of Cryptosporidium infection, considering pathogen removal efficiency, different exposure pathways and different susceptible subpopulations, was performed based on the result of a survey of source water from 66 waterworks in 33 major cities across China. The Cryptosporidium concentrations in source water were 0-6 oocysts/10 L, with a mean value of 0.7 oocysts/10 L. The annual diarrhea morbidity caused by Cryptosporidium in drinking water was estimated to be 2701 (95% confidence interval (CI): 138-9381) cases per 100,000 immunodeficient persons and 148 (95% CI: 1-603) cases per 100,000 immunocompetent persons, giving an overall rate of 149.0 (95% CI: 1.3-606.4) cases per 100,000 population. The cryptosporidiosis burden associated with drinking water treated with the conventional process was calculated to be 8.31 × 10(-6) (95% CI: 0.34-30.93 × 10(-6)) disability-adjusted life years (DALYs) per person per year, which was higher than the reference risk level suggested by the World Health Organization (WHO), but lower than that suggested by the United States Environmental Protection Agency (USEPA). Sixty-six percent of the total health burden due to cryptosporidiosis that occurred in the immunodeficient subpopulation, and 90% of the total DALYs was attributed to adults aged 15-59 years. The sensitivity analysis highlighted the great importance of stability of the treatment process and the importance of watershed protection. The results of this study will be useful in better evaluating and reducing the burden of Cryptosporidium infection.