Inactivation of Cryptosporidium parvum oocysts with chlorine dioxide

The effect of solution pH and temperature on the rate of inactivation of Iowa strain Cryptosporidium parvum (C. parvum) oocysts with chlorine dioxide was determined. Oocyst viability was assessed with a modified in vitro excystation method consistent with animal infectivity data. Inactivation curves were characterized by a lag phase followed by Chick–Watson first order kinetics. The rate of inactivation was essentially the same at pH 6 and 8. CT requirements at pH 10 were approximately 20–30% lower than those at pH 6–8. The magnitude of the lag phase and the inactivation rate constant were both found to obey Arrhenius law for the experimental temperature range of 4–30°C. CT requirements for C. parvum oocyst inactivation were found to increase by an average factor of approximately 3.4 for every 10°C decrease in temperature.