MOFIDI ET AL | PEER-REVIEWED | JOURNAL AWWA | JUNE 2001 95 disinfection Disinfection of Cryptosporidium parvum WITH polychromatic UV light Bench-scale experiments determined the germicidal effects of varying dosages of polychromatic ultraviolet (UV) radiation on oocysts of Cryptosporidium parvum. C. parvum oocysts suspended in treated surface water were irradiated with polychromatic light emitted by either a medium-pressure, continuous-wave UV lamp or a pulsed-UV lamp then assayed with human cell culture techniques. Experiments conducted using pulsed-UV doses of  16 mJ/cm 2 provided > 2-log inactivation of suspended oocysts of C. parvum. Experiments at lower UV dosages established a dose–response relationship with both the medium-pressure and pulsed-UV lamps. When disinfection results from both light sources were compared on an equivalent dosage basis, no statistical difference in disinfection power was found between the medium-pressure and pulsed-UV lamps. Results from both lamps showed that UV doses as low as 7.5 and 11 mJ/cm 2 provided inactivation of infectious oocysts of C. parvum at rates of 1 log (90%) and 2 log (99%), respectively. The authors also examined UV disinfection of heterotrophic bacteria and Escherichia coli. They found the response of heterotrophic bacteria to be statistically different from that of C. parvum, whereas E. coli ‘s response to UV light did not statistically differ from that of C. parvum. This suggests that E. coli may be a surrogate organism for C. parvum disinfection provided by UV technologies. BY ALEXANDER A. MOFIDI, HÉLÈNE BARIBEAU, PAUL A. ROCHELLE, RICARDO DE LEON, BRADLEY M. COFFEY, AND JAMES F. GREEN he protozoan parasite Cryptosporidium parvum is an important etiologic agent of waterborne disease outbreaks. C. parvum is of major concern because of (1) its high resistance to chlorine-based disinfectants at the dosages applied in treatment plants, (2) its low infectious dosage, and (3) the unavailability of drugs approved for prophylaxis or therapy. Cryp- tosporidiosis can lead to severe illness and even death in individuals whose immune systems are compromised. More than 50 documented outbreaks of cryp- tosporidiosis have been documented, with human infections per outbreak rang- T