Assessing the risk of infectious Cryptosporidium in drinking water

Abstract

Treated drinking water from 14 surface water treatment plants serving a combined population of approximately 9 million people was monitored for infectious Cryptosporidium oocysts using immunofluorescence microscopy to detect infections in cell culture. No infectious oocysts were detected in 370 samples with a total filtered volume of 349,053 L. The calculated risk of waterborne Cryptosporidium infection for the communities served by the 14 sampled plants was < 1 in 10,000. However, more accurate risk assessments of the threat to public health posed by Cryptosporidium in drinking water are still needed. 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.