Time and Temperature Effects on the Viability and Infectivity of Cryptosporidium parvum Oocysts in Chlorinated Tap Water

The authors compared the viability and infectivity of Cryptosporidium parvum oocysts in chlorinated tap water at various storage durations (i.e., 2 wk, 4 wk, 6 wk, or 8 wk) and at 2 cool temperatures (i.e., 10[ddot]C and 4[ddot]C), using in vitro (excystation) and in vivo (suckling mouse) methods. After 8 wk, mean oocyst excystation decreased to 33.4% and 26.7% at 10[ddot]C and 4[ddot]C, respectively. Suckling mice infectivity was higher after storage at 10[ddot]C than after storage at 4[ddot]C. These data suggest that Cryptosporidium parvum oocysts can survive and remain infectious for 8 wk in cool chlorinated tap water.