Refractory ceramic fiber exposure and pleural plaques

Our plain-English summary of Refractory ceramic fiber exposure and pleural plaques, by J. Lockey, G. Lemasters, C. Rice, et al (American Journal of Respiratory and Critical Care Medicine, 1996).

The study

• Authors: J. Lockey, G. Lemasters, C. Rice, K. Hansen, L. Levin, R. Shipley, H. Spitz, J. Wiot
• Journal: American Journal of Respiratory and Critical Care Medicine
• Published: 1996;154(5):1405-10
• Cited by: 39 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Refractory ceramic fibers (RCF) are manmade vitreous fibers (MMVF) manufactured for high-temperature applications. Between 1987 and 1992, a retrospective cohort and nested case-control study evaluated chest radiographs 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 modeled with three variables: years since first fiber production job, years in fiber production, and cumulative fiber exposure to date of study X-ray. The case-control study used a comprehensive characterization of 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 pleural thickening. Nine of 72 workers (12.5%) with more than 20 yr since their 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; 95% CI = 3.6 to 137.0). Similarly, adjusted ORs demonstrated a progressive relationship between cumulative fiber-months per milliliter (fiber-mo/ml) exposure and plaques. The case-control study confirmed that asbestos exposure did not account for the observed association between fiber exposure and plaques. A validity review of historical films demonstrated biologic plausibility for the association, since sufficient latency existed from the time of first RCF exposure to the development of plaques. There was no significant increase in parenchymal changes consistent with interstitial fibrosis.

In plain English

This study examined chest X-rays, taken between 1987 and 1991, of 652 current and former workers at two plants making refractory ceramic fibers (RCF). These are man-made vitreous fibers used for high-temperature insulation. Neither plant used asbestos in any product. Twenty workers (3.1%) had pleural changes: 19 had pleural plaques and one had diffuse pleural thickening. The authors compared production workers with nonproduction workers, adjusting for years since first reported asbestos exposure. Plaques were more common among workers whose first production job was more than 20 years earlier (9 of 72, 12.5%; odds ratio 9.5, 95% CI 1.9 to 48.2). They were also more common among those with more than 20 years in production (5 of 19, 26.3%; odds ratio 22.3, 95% CI 3.6 to 137.0). Odds ratios also rose with cumulative fiber exposure, though the confidence intervals overlapped. In a nested case-control analysis, the association persisted after accounting for possible past asbestos exposure. Three former production workers had lung-tissue (parenchymal) changes, which the authors reported was not a significant increase. The authors concluded that their findings support a causal hypothesis for RCF exposure and pleural plaques.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Retrospective cohort study with a nested case-control study (to account for past asbestos exposure) and a review of older chest films to check the timing of plaque appearance
• Who was studied: 652 current and former workers at two refractory ceramic fiber manufacturing plants. Of 868 eligible, 801 were interviewed and 81 sales engineers were excluded, leaving 720. Of these, 652 provided a front and two oblique chest X-rays taken between 1987 and 1991
• Exposure: Refractory ceramic fibers (man-made vitreous fibers), measured three ways: years since first RCF production job, years in RCF production, and cumulative exposure in fiber-months per milliliter. Asbestos was not used in manufacture at the plants. Workers' possible asbestos exposure from other jobs or home activities was assessed separately
• Main results:
  • Among all 652 workers, 20 (3.1%) had pleural changes on their X-rays: 19 pleural plaques and one diffuse pleural thickening
  • Odds ratios for the production categories were calculated against nonproduction workers and adjusted for years since first reported asbestos exposure
  • Among workers whose first RCF production job was more than 20 years earlier, 9 of 72 (12.5%) had plaques (odds ratio 9.5 compared with nonproduction workers; 95% CI 1.9 to 48.2)
  • Among workers with more than 20 years in RCF production work, 5 of 19 (26.3%) had plaques (odds ratio 22.3 compared with nonproduction workers; 95% CI 3.6 to 137.0)
  • Plaque rates were 0.3%, 5.3%, 6.4% and 7.8% in four cumulative exposure groups: more than 0 to 15, more than 15 to 45, more than 45 to 135, and more than 135 fiber-months per milliliter. Compared with the lowest group, the odds ratios for the three higher groups were 15.4, 21.3 and 24.2, all significant at p less than 0.05
  • In the nested case-control analysis, the association between RCF exposure measures and pleural plaques persisted after adding years since first reported asbestos exposure, or an asbestos exposure rating, to the model. One case with extensive asbestos exposure and that case's three controls were excluded
  • In a review of 205 older chest films for 18 of the plaque cases, only one case showed a plaque on an older film taken less than 5 years after starting RCF production work
  • Parenchymal (lung tissue) changes of profusion category 1/0 or greater were found in three former production workers. The authors reported no significant increase in parenchymal changes consistent with interstitial fibrosis
• The authors' conclusion: The authors concluded that the cohort study, the nested case-control study and the review of older films support a causal hypothesis for RCF exposure and the development of pleural plaques
• Limitations the authors state:
  • Odds ratios rose across the cumulative exposure groups, but the 95% confidence intervals for these groups overlapped
  • Cases and controls could not be matched on age because age was correlated with duration of employment, so current or former employment status was used instead
  • Risk among employees who always worked at lower RCF exposure levels could not yet be evaluated. The authors said this will become possible with continued surveillance

Topics

Medical terms in this study, explained in our Lexicon: Pleural Plaques, Vitreous, nested case-control study, Chest X-Ray, Case-Control Study, Asbestos Exposure, Diffuse Pleural Thickening, Odds Ratio.

Related studies

• Biopersistence of refractory ceramic fiber in human lung tissue and a 20-year follow-up of radiographic pleural changes in workers — J.E. Lockey, V.L. Roggli, et al. (2012)
• Potential significance of airborne fiber dimensions measured in the U.S. refractory ceramic fiber manufacturing industry — T.J. Lentz, C.H. Rice, et al. (1999)
• Mechanism of refractory ceramic fiber- and rock wool-induced cytotoxicity in alveolar macrophages — K.A. Kim, W.K. Lee, et al. (2001)
• Refractory ceramic fiber (RCF) toxicity and epidemiology: a review — M.J. Utell, L.D. Maxim (2010)
• Risk analysis for mortality from respiratory tumors in a cohort of refractory ceramic fiber workers — A.M. Walker, L.D. Maxim, et al. (2002)
• Perspectives on refractory ceramic fiber (RCF) carcinogenicity: comparisons with other fibers — H. Greim, M.J. Utell, et al. (2014)

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