Waterborne giardiasis in the United States: a review

Twenty-three waterborne outbreaks of giardiasis have been reported in the US, 1972-77. Data indicate that disinfection as the only treatment for surface water sources is ineffective in preventing waterborne transmission of this organism. To protect against transmission, all surface water should receive chemical pretreatment, preferably with sedimentation, and filtration in addition to disinfection. Outbreak data indicate that negative coliform tests do not provide assurance that water is free of Giardia cysts.