REFRACTORY CERAMIC FIBER EXPOSURE AND PLEURAL PLAQUES

Refractory ceramic fibers (RCF) are manmade vitreous fibers (MMVF) man ufactured for high-temperature applications. Between 1987 and 1992, a retrospective cohort and nested case-control study evaluated chest rad iographs from 652 workers involved in the manufacture of these fibers for plausibility of a causal relationship between exposure to RCF and chest-radiographic changes. The exposure-response relationship was mod eled with three variables: years since first fiber production job, yea rs in fiber production, and cumulative fiber exposure to date of study X-ray. The case-control study used a comprehensive characterization o f possible asbestos exposure to investigate asbestos as the potential causative agent of chest-radiographic changes. Chest radiographs of 20 workers (3.1%) demonstrated 19 pleural plaques and one diffuse pleura l thickening. Nine of 72 workers (12.5%) with more than 20 yr since th eir first fiber-production job had plaques (odds ratio [OR] = 9.5; 95% confidence interval [CI] = 1.9 to 48.2). Five of 19 workers with more than 20 yr in fiber-production work (26.3%) had plaques (OR = 22.3; 9 5% CI = 3.6 to 137.0). Similarly, adjusted ORs demonstrated a progress ive relationship between cumulative fiber-months per milliliter (fiber -mo/ml) exposure and plaques. The case-control study confirmed that as bestos exposure did not account for the observed association between f iber exposure and plaques. A validity review of historical films demon strated biologic plausibility for the association, since sufficient la tency existed from the time of first RCF exposure to the development o f plaques. There was no significant increase in parenchymal changes co nsistent with interstitial fibrosis.