Purified Cryptosporidium parvum oocysts were exposed to ozone, chlorine dioxide, chlorine, and monochloramine. Excystation and mouse infectivity were comparatively evaluated to assess oocyst viability. Ozone and chlorine dioxide more effectively inactivated oocysts than chlorine and monochloramine did. Greater than 90% inactivation as measured by infectivity was achieved by treating oocysts with 1 ppm of ozone (1 mg/liter) for 5 min. Exposure to 1.3 ppm of chlorine dioxide yielded 90% inactivation after 1 h, while 80 ppm of chlorine and 80 ppm of monochloramine required approximately 90 min for 90% inactivation. The data indicate that C. parvum oocysts are 30 times more resistant to ozone and 14 times more resistant to chlorine dioxide than Giardia cysts exposed to these disinfectants under the same conditions. With the possible exception of ozone, the use of disinfectants alone should not be expected to inactivate C. parvum oocysts in drinking water.

An existing method for the detection of Cryptosporidium oocysts in water was modified to investigate oocyst prevalence in large volumes of water. Surface waters and sewage effluents were filtered, eluted from the filter, and concentrated using centrifugation. The resultant pellet was then homogenized, sonicated, and placed on a sucrose gradient to separate oocysts from the sediment. The uppermost gradient layer was then examined by immunofluorescence using a labeled monoclonal antibody. Using this technique, average numbers of oocysts detected in raw and treated sewage were 5.18 X 10(3) and 1.30 X 10(3)/L, respectively. Filtered sewage effluents had significantly lower numbers of oocysts (10.0/L). These data show that sand filtration may reduce the concentrations of this parasite in waste waters. Highly variable oocyst numbers were encountered in surface waters. Since Cryptosporidium oocysts are frequently present in environmental waters, they could be responsible for waterborne outbreaks of disease.

Cryptosporidium is a coccidian protozoan and has recently been recognized as a cause of human gastroenteritis. The illness may be severe in immunocom-promised individuals and can result in death. The organism is monoxenous, and infective oocysts are shed in the feces, which are transmitted via the fecal-oral route. Therefore, Cryptosporidium may be a possible candidate as an etiological agent of waterborne or foodborne disease. Previously, the lack of methods for detection of this organism in diarrheal samples as well as environmental samples, has made it difficult to substantiate this premise. Detection of Cryptosporidium oocysts in water has now been accomplished using a filtration-elution procedure. A fluorescently-labelled monoclonal antibody which has been used for the detection of Cryptospori di urn in feces was also used to detect the oocysts in environmental samples. The method developed for detection of Cryptosporidium in water including: 1) filtration with polypropylene cartridge filters, 2) elution with Tween 80/detergent, 3) concentration with Sheather's flotation, and 4) detection on membrane filters, was evaluated and used to examine wastewater and fresh water for Cryptosporidiurn oocyst concentrations. Recovery from the sucrose gradient step averaged 72 – 82%. Overall recovery efficiencies ranged from 25 – 82% (average 50%), but were diminished with low seeds. Concentrations were found in ranges from 60 to 52,000 oocysts/gal in treated and raw sewage. In fresh water, oocysts numbered 8 to 22,000/gal and were concentrated in rapid sand filters averaging 59,000/gal in the backflush. Cryptosporidium may now be considered a potential waterborne parasite.