Serological Evidence of Endemic Waterborne Cryptosporidium Infections

PURPOSE: Cryptosporidium oocysts are commonly detected in surface-derived drinking water, however, the public health significance of these findings is unclear. This study compared the evidence of prior Cryptosporidium infection for people drinking water derived from surface versus ground water sources. METHODS: This study measured serological responses to two Cryptosporidium antigen groups for blood donors from two midwestern United States cities with different drinking water sources: filtered and chlorinated river water receiving agricultural and domestic sewage upstream versus chlorinated water from an underground aquifer. Initial and nine-month paired serological responses to two Cryptosporidium antigen groups were compared. RESULTS: Initially, donors from the surface water city had a higher relative prevalence (RP) of a serological response (54% vs 38%, RP = 1.39 (1.21,1.60)). Donors with a detectable baseline response who resided in the surface water city had a higher relative risk (RR) of an increased intensity of response on the follow-up blood draw (15/17-kDa, 40/100 vs 11/100, RR = 3.78 (1.89,7.58)), (27-kDa 38/100 vs 18/100, RR = 2.07 (1.31,3.25)). Donors with no baseline response to the 15/17-kDa marker who resided in the surface water city also had a higher risk of serconversion (38/100 vs 14/100, RR = 2.63 (1.78,3.91)). CONCLUSIONS: These rates of both background and drinking water related Cryptosporidium infections are substantially higher than previously estimated, however, the risk of illness from infection may be lower.