Improved cell culture immunofluorescent assay for detection of infectious Cryptosporidium spp. in prefinished water

Abstract

The New York City Department of Environmental Protection's (NYC) Hillview Reservoir is an uncovered prefinished water storage reservoir postultraviolet (post-UV) light disinfection. As an additional tool to the detection of total (viable and nonviable) oocysts using Methods 1623/1623.1, the performance of an improved cell culture immunofluorescent assay (CC-IFA) for the specific detection of infectious oocysts in this NYC reservoir matrix was evaluated. Mean CC-IFA matrix spike recovery of infectious Cryptosporidium parvum and Cryptosporidium hominis oocysts was comparable to the mean Method 1623 recovery of total oocysts, ranging from 29 to 46%. Experiments using ≤5 C. parvum or ≤10 C. hominis viable oocyst spikes prepared using flow cytometry indicated that the reservoir matrix did not adversely affect CC-IFA detection. Therefore, the improved CC-IFA appears useful for the detection of environmentally relevant, low numbers of infectious oocysts in the reservoir matrix and for the refined assessment of Cryptosporidium risk.