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APHA Scientific Session and Event Listing

Theodore Larson, MS, Maureen Phelan, MS, and Natalia Melnikova, MD, PhD. Division of Health Studies, Centers for Disease Control and Prevention/Agency for Toxic Substances and Disease Registry, 1600 Clifton Rd, Mail Stop E-31, Atlanta, GA 30333, 404-498-0593, THL3@cdc.gov

Malignant mesothelioma (MM) is an uncommon fatal tumor with a long latency period and is usually associated with asbestos exposure. To examine the relationship between asbestos exposure and mesothelioma mortality, we conducted a retrospective cohort study of workers exposed to amphibole-contaminated vermiculite between 1935 and 1993. We used a job exposure matrix that took into account industrial hygiene measurements to estimate cumulative asbestos exposure for each worker in the cohort (n=1,862). Using cumulative asbestos exposure (CAE) as a time-dependent covariate of mortality, we estimated mesothelioma hazard ratios using Cox proportional hazards models. Preliminary results of this study will be presented.

The hazard of mortality in the mesothelioma model increased significantly with CAE. The model predicts hazard ratios that are near but above 1.0 up to about 10 fiber-years (f-y), after which the hazard ratios separate and increase exponentially with CAE. At 500 f-y, these models predict hazard ratio of 1.8 for mesothelioma deaths.

The exponential increase in the hazard ratio estimates suggests individuals exposed to relatively high levels of the amphibole in vermiculite mined in Libby, Montana, are at much greater risk of mesothelioma-related mortality than those with lower exposure. However, the model suggests that there is no exposure threshold below which there is no increased risk of mesothelioma-related mortality. This may have implications for persons with low-level exposure to Libby vermiculite.

Learning Objectives:

• To study the relationship between asbestos exposure and mesothelioma mortality in workers exposed to amphibole-contaminated vermiculite

Keywords: Mortality, Occupational Exposure

Presenting author's disclosure statement:

Not Answered