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INFLUENCE OF EXPOSURE ASSESSMENT METHOD IN AN EPIDEMIOLOGIC STUDY OF TRIHALOMETHANE EXPOSURE AND SPONTANEOUS ABORTION
Waller, K., S. Swan, G. Windham, AND L. Fenster. INFLUENCE OF EXPOSURE ASSESSMENT METHOD IN AN EPIDEMIOLOGIC STUDY OF TRIHALOMETHANE EXPOSURE AND SPONTANEOUS ABORTION. Presented at 2001 Epidemiology congress, Toronto, Canada, June 13, 2001.
Trihalomethanes are common contaminants of chlorinated drinking water. Studies of their health effects have been hampered by exposure misclassification, due in part to limitations inherent in using utility sampling records. We used two exposure assessment methods, one based on utility-wide sampling averages, and one based on measurements from the utility sampling site closest to the subject's residence, to re-estimate total trihalomethane (TTHM) exposure for 4,212 participants in a pre-existing study of risk factors for spontaneous abortion (SAB). For both approaches we performed unweighted, weighted, and subset analyses. The weighted and subset analyses were intended to reduce exposure misclassification, and were based on within-utility variance in TTHM measurements for the utility-wide average approach, and the distance between the subject's residence and sampling site for the closest-site approach. In general, odds ratios obtained using the utility-wide average, but not the closest-site, approach became progressively stronger in the weighted and subset analyses. A dose-response was seen between SAB and an exposure metric incorporating both TTHM concentration (utility-wide average approach) and personal ingestion, with SAB rates ranging from 8.3-13.7% (unweighted), 7.9-16.6% (variance weighted), and 6.6-23.1% (low-variance subset). Utility-wide average TTHM exposure assessment methods together with variance-based weights and subsets are relatively simple exposure assessment techniques which may increase the epidemiologic usefulness of utility sampling records.
This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.