Inactivation of Cryptosporidium parvum oocysts with ozone

Ozone inactivation rates for Cryptosporidium parvum (C. parvum) oocysts were determined with an in vitro excystation method based on excysted sporozoite counts. Results were consistent with published animal infectivity data for the same C. parvum strain. The inactivation kinetics for C. parvum were characterized by a lag phase followed by pseudo-first order kinetics. Both the magnitudes of the lag phase and the pseudo-first order rate constant were found to be different for C. parvum oocysts from two different sources, and to obey Arrhenius law for the experimental temperature range of 5–30°C. CT requirements for C. parvum inactivation were found to increase by an average factor of approximately three for every 10°C decrease in temperature.