Assessing the risk of infectious Cryptosporidium in drinking water

Treated drinking water from 14 surface water treatment plants serving a combined population of approximately 9 million people was monitored for infections Cryptosporidium oocysts using immunofluorescence microscopy to detect infections in cell culture. No infectious oocysts were detected in 349,053 L from 370 samples. The calculated risk of waterborne Cryptosporidium infection based on the lack of positives, total volume sampled, and assumptions about daily volume of water consumption was < 1 in 10,000. However, further study to establish more accurate risk assessments of the threat to public health posed by Cryptosporidium in drinking water is still needed, because results from 14 plants cannot be extrapolated to the entire United States. This study demonstrated that routine infectivity monitoring of large volumes of treated drinking water is feasible. Consequently, testing finished water for infectious Cryptosporidium should be considered during periods of regulatory monitoring, such as the second round of the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR).