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UNC-Chapel Hill ENVR 890 - Inferences Drawn from a Risk Assessment Compared Directly with a Randomized Trial

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Continued reporting of outbreaks of diseasefrom consumption of drinking water (Barwicket al. 2000; Lee et al. 2002; Levy et al. 1998;Yoder et al. 2004) in the United States hasfueled the need for regulatory action throughrisk assessments as mandated by the SafeDrinking Water Act (SDWA 1996). Riskassessments historically have been used toevaluate the health risks of properly treateddrinking water because of the general beliefthat drinking water risks were too low to bedetected through epidemiology studies.Recent drinking water intervention trials,however, have begun to question the assump-tion that there is little or no risk of infectiousgastrointestinal (GI) illness attributable to theconsumption of drinking water when watertreatment systems are functioning properly(Payment et al. 1991, 1997). In contrast,other trials have suggested that there is little orno risk (Colford et al. 2005; Hellard et al.2001). Based on these findings and inresponse to the 1996 Congressional amend-ment to the SDWA that emphasizes the needfor sound science and risk-based standard set-tings [U.S. Environmental Protection Agency(EPA) 1989], there has been increased interestin evaluating methodologies to help estimatethe risk of GI illness attributable to drinkingwater in communities. In the present study wecompare and contrast two approaches for theassessment of risk of diarrhea caused by drink-ing water—a microbial risk assessment and arandomized intervention trial design.Using data collected in Davenport, Iowa(Colford et al. 2005), we compared the twotechniques to estimate the risk from waterbornepathogens due to exposure to drinking water.For this study, risk assessment is based on theintegration of several independent sources ofexposure information to estimate dose (i.e.,water quality, drinking water treatment plantefficiency, and tap water consumption pat-terns). We then used the dose information in ahealth effects model to predict the risk of illnessdue to drinking tap water. The randomizedintervention trial directly measures the impactof drinking water on diarrhea and compares theincidence of GI illness between interventionand control subjects.Both approaches have wide appeal. Therandomized trial is considered the “gold stan-dard” for providing unconfounded causal riskestimates associated with a particular expo-sure. When lacking these direct estimates ofrisk, quantitative risk assessment is the pre-ferred method for attaining risk estimates andis used by the U.S. EPA, U.S. Food andDrug Administration, World Health Organi-zation, and other stakeholders for regulatory and operational purposes. Although theseapproaches are widely accepted, they also havemany limitations. Low sensitivity because ofsample size constraints, and biases due to bothexposure and outcome misclassification mustbe acknowledged when interpreting random-ized trial results. Similarly, risk assessments aremodel-based estimates and rely on water qual-ity data as input, and so must be interpreted inthis context. Both approaches have theirstrengths and weaknesses. In the present studyour goal was to compare and contrast the twoapproaches for obtaining estimates of drinkingwater risk when coincident data are available.Several authors have proposed methods forestimating the risk of drinking water (Haaset al. 1993; Messner et al. 2001; Regli et al.1999). Our study differs from these previousstudies in that we incorporated additionaldetailed local information relevant to riskassessment, including measurements ofpathogen levels in the source water over a1-year period, pathogen removal efficiency ofthe Davenport drinking water treatment plant(which uses sedimentation, filtration, andchlorine disinfection), and data on local tapwater consumption.Materials and MethodsAttributable risk from intervention trial(Davenport, Iowa). The study design of theintervention trial in Davenport is similar tothose of previously published drinking waterintervention trials (Colford et al. 2002;Hellard et al. 2001; Payment et al. 1991,1997). Unlike prior randomized trials, how-ever, a crossover design was used where, foreach intervention period (~ 6 months), half theenrolled cohort had a water treatment deviceEnvironmental Health Perspectives•VOLUME 114 | NUMBER 8 | August 20061199ResearchAddress correspondence to J.N.S. Eisenberg,Department of Epidemiology, School of PublicHealth, University of Michigan, 611 Church St.,Ann Arbor, MI 48104 USA. Telephone: (734) 615-1625. Fax: (734) 998-6837. E-mail: [email protected] acknowledge A. Phipps and M. Birkner for con-ducting the preliminary simulations and C. Wrightfor final editing and formatting.This work was partially supported by cooperativeagreement U50/CCU916961 from the CDC andpartially by grant RD-83172701 from the U.S. EPA. The authors declare they have no competingfinancial interests.Received 25 September 2005; accepted 4 April 2006.Inferences Drawn from a Risk Assessment Compared Directly with a Randomized Trial of a Home Drinking Water InterventionJoseph N.S. Eisenberg,1Alan Hubbard,2Timothy J. Wade,3Matthew D. Sylvester,2Mark W. LeChevallier,4Deborah A. Levy,5and John M. Colford Jr.21Department of Epidemiology, School of Public Health, University of Michigan, Ann Arbor, Michigan, USA; 2Center for Occupational and Environmental Health and Division of Epidemiology and Environmental Health Sciences, School of Public Health, University ofCalifornia–Berkeley, Berkeley, California, USA; 3National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Chapel Hill, North Carolina, USA; 4American Water, Voorhees, New Jersey,USA; 5Division of Healthcare Quality Promotion, National Center of Infectious Diseases, Centers for Disease Control and Prevention,Atlanta, Georgia, USARisk assessments and intervention trials have been used by the U.S. Environmental Protection Agencyto estimate drinking water health risks. Seldom are both methods used concurrently. Between 2001and 2003, illness data from a trial were collected simultaneously with exposure data, providing aunique opportunity to compare direct risk estimates of waterborne disease from the intervention trialwith indirect estimates from a risk assessment. Comparing the group with water treatment (active)with that without water treatment (sham), the estimated annual attributable disease rate (cases per10,000 persons per year) from the trial provided no evidence of a


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UNC-Chapel Hill ENVR 890 - Inferences Drawn from a Risk Assessment Compared Directly with a Randomized Trial

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