Protozoa Co-Occurrence in Surface Water Sources of Drinking Water

• Activity Number: 195
• Type: Contributed
• Date/Time: Monday, August 5, 2013 : 10:30 AM to 12:20 PM
• Sponsor: Section on Statistics and the Environment
• Author(s): Michael Messner*+
• Companies: U.S. Environmental Protection Agency
• Keywords: Bayesian ; Water ; Risk ; Disease

Abstract

Under EPA's "ICR Supplemental Surveys", 87 drinking water treatment plants assayed their source waters monthly for both Cryptosporidium and Giardia over a period of 18 months. EPA utilized the Cryptosporidium data to estimate the costs and benefits of its Long-Term 2 (LT2) Enhanced Surface Water Treatment Rule. This paper begins with a review of the Cryptosporidium modeling to estimate the Rule's effectiveness at reducing consumer exposure to the pathogen. Because the Rule required corrective action for plants with high levels of Cryptosporidium, it is not surprising that even a small percentage of plants taking action could yield a large reduction in total exposure to Cryptosporidium. This new analysis includes Giardia and its covariance with Cryptosporidium, and is used to predict the Rule's effectiveness at reducing exposures to Giardia. Although not specifically targeted by the Rule, percentage reduction of Giardia exposures appear to be nearly as great as those for Cryptosporidium. The large reduction in Giardia exposure may be responsible for a significant number of illnesses avoided, a previously nonquantified benefit of the LT2 Rule.