Distribution of Cryptosporidium oocysts in a water supply

Cryptosporidium has emerged as a significant waterborne pathogen. Methods have been developed for analysis of this organism using immunofluorescence counts. In this paper, we report on the results of a one year sequence of weekly samples in the water supply of a relatively high-quality water system in the Northwest United States. The results show consistency with the Poisson distribution, indicating that, at least for high-quality water, the theoretical minimum variability can be attained. This will assist in the interpretation of results from diverse systems contemplated under future monitoring activities.