An epidemiological study of the respiratory health of workers in the European refractory ceramic fibre industry

Our plain-English summary of An epidemiological study of the respiratory health of workers in the European refractory ceramic fibre industry, by H.A. Cowie, P. Wild, J. Beck, et al (Occupational and Environmental Medicine, 2001).

The study

• Authors: H.A. Cowie, P. Wild, J. Beck, G. Auburtin, C. Piekarski, N. Massin, J.W. Cherrie, J.F. Hurley, B.G. Miller, S. Groat, C.A. Soutar
• Journal: Occupational and Environmental Medicine
• Published: 2001;58(12):800-10
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To investigate possible relations between respiratory health and past airborne exposure to refractory ceramic fibres (RCFs) and respirable dust in workers at six European factories, studied previously in 1987.

Methods: The target population comprised all current workers associated with RCF production, plus others who had participated in 1987 "leavers". Information was collected on personal characteristics, chest radiographs, lung function, respiratory symptoms, smoking, and full occupational history. Regression analysis was used to study relations between indices of health of individual workers and of cumulative exposure to airborne dust and fibres, and likely past exposure to asbestos.

Results And Discussion: 774 workers participated (90% of current workers, 37% of leavers). Profusion of small opacities in exposed workers (51% 0/1+; 8% 1/0+) was similar to that among an unexposed control group but higher than in new readings of the 1987 study films (11% 0/1+, 2% 1/0+). The large difference between 1987 and recent films may be, at least in part, a reading artefact associated with film appearance. Small opacities of International Labour Organisation (ILO) category 1/0+ were not associated with exposure. An association of borderline significance overall between 0/1+ opacities and exposure to respirable fibres was found for some exposure periods only, the time related pattern being biologically implausible. Pleural changes were related to age and exposure to asbestos, and findings were consistent with an effect of time since first exposure to RCFs. Among men, forced expired volume in 1 second (FEV(1)) and forced vital capacity (FVC) were inversely related to exposure to fibres, in current smokers only. FEV(1)/ FVC ratio and transfer factor (TL(CO)) were not related to exposures. The estimated restrictive effect was on average mild. Prevalence of respiratory symptoms was low. Chronic bronchitis and its associated symptoms (cough, phlegm) showed some association with recent exposure to respirable fibres. This could be due to an irritant effect of RCFs.

In plain English

This cross sectional study examined the respiratory health of 774 workers (692 men, 82 women) at six refractory ceramic fibre (RCF) plants in England, France and Germany. Participants included 90% of current workers and 37% of past workers seen in a 1987 survey. The authors estimated each worker's cumulative exposure to fibres and dust and recorded possible past asbestos exposure. Small lung opacities of category 0/1 or more appeared on 51% of exposed workers' X-rays, the same as in an unexposed comparison group. Category 1/0 or more opacities were not associated with exposure. Among 355 workers with no occupational asbestos exposure, pleural changes were associated with time since first RCF exposure after adjustment for age, but pleural plaques alone were not significantly associated. Among male current smokers only, two breathing measures (FEV1 and FVC) were lower with higher fibre exposure, by about 100 ml at average exposure. Recurrent chest illness was associated with cumulative fibre exposure. The authors called these relations relatively mild and in some cases ambiguous. They noted that exposure estimates before 1987 were much less reliable.

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: Cross sectional morbidity study (second survey of a workforce first studied in 1987), with chest radiographs, lung function tests, symptom questionnaires and estimated individual exposure indices
• Who was studied: 774 workers (692 men, 82 women) out of 1006 eligible, at six RCF plants (two in England, three in France, one in Germany). This was 90% of eligible current workers and 37% of 'leavers' from the 1987 survey. Statistical analyses of small opacities were restricted to men.
• Exposure: Estimated cumulative exposure to respirable and non-respirable refractory ceramic fibres and to respirable and total dust. The mean cumulative respirable fibre exposure was 4.9 (range 0.01 to 36) fibres per ml-years. Possible asbestos exposure was also classified: 158 (20%) within the RCF industry and 351 (45%) outside it. Asbestos fibre types were not specified, and intensity of asbestos exposure was not available.
• Main results:
  • Small opacities of profusion 0/1 or more were found in 51% of the RCF-exposed study population, the same prevalence as in the external group of non-exposed workers. Re-readings of the 1987 films of RCF workers showed 11%.
  • Among men, small opacities category 1/0 or more were not associated with lifetime fibre exposure or time in production: OR 1.02 (95% CI 0.76 to 1.37) per 5 f.ml-1.y respirable fibres. They were associated with current smoking compared with non-smoking: OR 5.7 (95% CI 2.1 to 15.6).
  • Among men, the association between 0/1 or more opacities and respirable fibres was of borderline significance: OR 1.18 (95% CI 0.98 to 1.43) per 5 f.ml-1.y. The authors described the pattern across calendar periods as biologically implausible: effects were largest for the earliest years and the most recent years, and weakest in between.
  • Pleural changes of any kind were classified by two or more readers on 78 (11%) of current radiographs, and pleural plaques on 40 (5%).
  • Among 355 subjects not occupationally exposed to asbestos, and in a model including age, the odds ratios per 10 years since first RCF exposure were 2.22 (95% CI 1.17 to 4.24) for pleural changes and 2.03 (95% CI 0.78 to 5.25) for pleural plaques. Only nine of these subjects had plaques.
  • Among workers probably exposed to asbestos, the results depended on the asbestos index used. With adjustment for time since first asbestos exposure within the industry, there was a strong effect of asbestos and little evidence of an association between time since first RCF exposure and pleural plaques or changes.
  • Among male current smokers, FEV1 was inversely related to all exposure variables, most strongly to respirable fibres (−0.118 litres per 5 f.ml-1.y). FVC showed a similar pattern. The estimated effect was a loss of about 100 ml FEV1 or FVC for average exposure of 5 f.ml-1.y. No overall effect of exposure on transfer factor (TLCO) was found in men or women.
  • Respiratory symptoms were generally of low prevalence. Only 25 subjects reported chronic bronchitis, which was not significantly related to any exposure variable. Recurrent chest illness was significantly associated with cumulative exposure to respirable fibres: OR 1.48 (95% CI 1.11 to 1.96) per 5 f.ml-1.y.
• The authors' conclusion: The authors concluded that FEV1 and FVC in male current smokers were inversely related to cumulative respirable fibre exposure, suggesting a real but on average mild effect on lung function in smokers. They found no association of category 1/0 or more opacities with exposure. They considered the relations relatively mild and in some cases ambiguous, but judged it prudent to keep dust and fibre concentrations as low as possible and to discourage smoking.
• Limitations the authors state:
  • Exposure estimates before 1987 were much less reliable. 1987 concentrations were applied to earlier years, although earlier concentrations were widely thought to have been higher.
  • Less healthy workers may have left the industry, and participation of leavers was low. The authors judged that any resulting distortion of exposure-response findings was likely small.
  • Pleural findings were limited by co-exposure to asbestos and by the relative newness of the European RCF industry.
  • Detailed information on the intensity of asbestos exposure was not available.
  • The much lower prevalence of small opacities in the 1987 films was unexplained. The authors thought it may be principally a reading artefact related to film appearance.
  • Associations could not be convincingly attributed to fibres rather than dust, or the reverse.
  • Symptom associations might reflect workers in currently dusty jobs reporting more symptoms.
  • Results for women were based on small numbers.

Topics

Medical terms in this study, explained in our Lexicon: Chest X-Ray, Occupational History, Cumulative Exposure.

Related studies

• An epidemiological study of the role of chrysotile asbestos fibre dimensions in determining respiratory disease risk in exposed workers — L. Stayner, E. Kuempel, et al. (2008)
• Exposure to refractory ceramic fibres in the metal industry — M. Linnainmaa, J. Kangas, et al. (2007)
• Respiratory impairments due to dust exposure: a comparative study among workers exposed to silica, asbestos, and coalmine dust — X. Wang, E. Yano, et al. (1997)
• Health effects of refractory ceramic fibres: scientific issues and policy considerations — L.R. Glass, R.C. Brown, et al. (1995)
• The effects of intrapleural injections of alumina and aluminosilicate (ceramic) fibres — G.H. Pigott, J. Ishmael (1992)
• Risk analysis for mortality from respiratory tumors in a cohort of refractory ceramic fiber workers — A.M. Walker, L.D. Maxim, et al. (2002)

Browse more research in Occupational and Environmental Medicine, or return to medical research.