A comparison of four fluorescent antibody-based methods for purifying, detecting, and confirming Cryptosporidium parvum in surface waters.

Cryptosporidiosis has been traced to drinking contaminated surface water, which was either not treated or was ineffectively treated. Testing to detect Cryptosporidium parvum in surface water has been suggested to help prevent future outbreaks. In the present study, the same sample collection and filtration methods were used to compared sample processing and detection steps from 4 testing methods: a modified information collection rule (ICR) method and method 1623 (both developed by the U.S. Environmental Protection Agency), a flow cytometric method, and a solid-phase cytometric method. All of these methods use fluorescent antibody staining, which is only a presumptive indication of the presence of this parasite. Confirmation requires another assay. Methods were evaluated for both presumptive and confirmed detection. Solid-phase cytometry had the highest presumptive and confirmed detection rates. Flow cytometry had the next highest presumptive detection rate in reagent water but was third in spiked surface and tap waters, with no confirmation procedure. The ICR method had the third highest presumptive detection rate in reagent water and the second highest in spiked surface and tap waters but failed to confirm any oocysts. Method 1623 had significantly lower presumptive detection than any other method and a significantly lower confirmation rate than the solid-phase cytometry method.