Waterborne transmission of Cryptosporidium, Cyclospora and Giardia.

Waterborne transmission of Cryptosporidium, Cyclospora, and Giardia has been associated with numerous recent outbreaks of diarrheal disease. Epidemiologic evidence shows that many community-acquired infections originate from public water sources. Drinking water, even when chlorinated and filtered, has been implicated in several outbreaks. Cryptosporidium and Cyclospora are resistant to chlorine. Giardia cysts are not killed immediately by chlorine and are less susceptible than most other organisms. Swimming pools and other recreational waters have also been implicated as transmission sources. All 3 organisms pose a challenge to the water industry, as they are difficult to detect in water when small numbers of cysts or oocysts are present. Small numbers of these organisms can cause disease; therefore, the clinical laboratory must be vigilant in screening, identifying, and reporting outbreaks of illness due to these protozoa.