Occupational exposure to asbestos and mortality among asbestos removal workers: a Poisson regression analysis

Our plain-English summary of Occupational exposure to asbestos and mortality among asbestos removal workers: a Poisson regression analysis, by G. Frost, A.H. Harding, A. Darnton, et al (British Journal of Cancer, 2008).

The study

• Authors: G. Frost, A.H. Harding, A. Darnton, D. McElvenny, D. Morgan
• Journal: British Journal of Cancer
• Published: 2008;99(5):822-9
• Cited by: 41 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The asbestos industry has shifted from manufacture to stripping/removal work. The aim of this study was to investigate early indications of mortality among removal workers. The study population consisted of 31 302 stripping/removal workers in the Great Britain Asbestos Survey, followed up to December 2005. Relative risks (RR) for causes of death with elevated standardised mortality ratios (SMR) and sufficient deaths were obtained from Poisson regression. Risk factors considered included dust suppression technique, type of respirator used, hours spent stripping, smoking status and exposure length. Deaths were elevated for all causes (SMR 123, 95% CI 119-127, n=985), all cancers including lung cancer, mesothelioma, and circulatory disease. There were no significant differences between suppression techniques and respirator types. Spending more than 40 h per week stripping rather than less than 10, increased mortality risk from all causes (RR 1.4, 95% CI 1.2-1.7), circulatory disease and ischaemic heart disease. Elevated mesothelioma risks were observed for those first exposed at young ages or exposed for more than 30 years. This study is a first step in assessing long-term mortality of asbestos removal workers in relation to working practices and asbestos exposure. Further follow-up will allow the impact of recent regulations to be assessed.

In plain English

This study examined deaths among workers only ever employed as asbestos strippers or removal workers in the Great Britain Asbestos Survey, followed up to December 2005. Among all 52,387 such workers, deaths from all causes were higher than expected from national rates (SMR 122.9, 95% CI 118.7–127.3; 3,165 deaths). The main analysis covered 31,302 workers who completed a detailed questionnaire. They had 985 deaths (SMR 111.3, 95% CI 104.4–118.4), including 384 cancers, 115 lung cancers and 23 mesotheliomas; mesothelioma deaths were counted only for 2001–2005. Risk did not differ significantly between wet and dry removal or between respirator types. Workers averaging 40 or more hours a week in the stripping enclosure had higher all-cause mortality than those averaging under 10 hours (RR 1.4, 95% CI 1.2–1.7). Their circulatory disease and ischaemic heart disease risks were also higher. Mesothelioma risk was higher for 30 or more years of exposure than for under 30 years (RR 7.3, 95% CI 2.5–21.6). The authors cautioned that follow-up was short given the long delay before asbestos diseases appear, and that much questionnaire data was missing.

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: Cohort mortality study: standardised mortality ratios (SMRs) compared with national death rates, plus Poisson regression to estimate relative risks within the cohort
• Who was studied: Workers only ever employed as asbestos strippers or removal workers in the Great Britain Asbestos Survey. The SMR analysis covered all 52,387 such workers (1971–2005). The Poisson regression covered the 31,302 who completed the more detailed questionnaire introduced after 1987. Deaths were followed up to December 2005.
• Exposure: Asbestos stripping and removal work. The article does not name fiber types. Factors studied were dust suppression method (wet or dry), respirator type, average weekly hours in the stripping enclosure, smoking status, age at first exposure, length of exposure, and whether first exposure came before or after the 1983 Asbestos Licensing Regulations (ALR).
• Main results:
  • All-cause deaths were raised among all 52,387 removal workers: 3,165 deaths, SMR 122.9 (95% CI 118.7–127.3). Among the 31,302 analysed workers there were 985 deaths, SMR 111.3 (95% CI 104.4–118.4).
  • Among the 31,302 analysed workers, the 985 deaths included 384 cancers, 115 lung cancers and 23 mesotheliomas.
  • Mesothelioma deaths were coded under ICD-10, so only those occurring from 2001 to 2005 were included in the analysis.
  • Mesothelioma deaths were raised. All removal workers had 69 deaths (SMR 808.2, 95% CI 628.8–1022.8). Analysed workers had 23 deaths (SMR 808.2, 95% CI 512.3–1212.7).
  • There were no statistically significant differences in risk between mainly wet and dry removal methods. No significant association was seen between the main respirator used and risk for any of the diseases studied.
  • Workers averaging more than 40 hours a week in the stripping enclosure, compared with those averaging less than 10 hours, had higher risks of death: all causes RR 1.4 (95% CI 1.2–1.7), circulatory disease RR 1.7 (95% CI 1.2–2.4), ischaemic heart disease RR 1.9 (95% CI 1.2–2.8).
  • The proportion of current smokers rose with hours spent in the enclosure. Adjusting for smoking weakened the hours results, but the increasing trend remained. These adjusted figures were not shown in the article.
  • Long-term workers (two or more medical examinations) had higher risks than short-term workers (one examination): all cancers RR 1.5 (95% CI 1.2–1.9), lung cancer RR 1.6 (95% CI 1.1–2.4), mesothelioma RR 4.5 (95% CI 1.3–16.0).
  • Mesothelioma risk was higher for workers with 30 or more years of exposure than for those with less than 30 years: RR 7.3 (95% CI 2.5–21.6).
  • Mortality risk for all cancers and for mesothelioma fell as age at first exposure rose. All-cause mortality was lower for those first exposed after age 50 than for those first exposed before age 20: RR 0.7 (95% CI 0.6–0.9).
  • Workers first exposed after the 1983 ALR had lower risks than those first exposed before it: all cancers RR 0.8 (95% CI 0.7–1.0), mesothelioma RR 0.2 (95% CI 0.04–0.6). The authors said this finding should be treated with caution.
• The authors' conclusion: The authors concluded that the risk of mortality increased as the number of hours spent removing asbestos increased. They also concluded that a link was suggested between hours in the stripping enclosure and smoking status.
• Limitations the authors state:
  • Follow-up since the 1983 regulations was still relatively short compared with the latency of asbestos-related diseases.
  • The lower risks seen for workers first exposed after the 1983 regulations should be treated with caution.
  • Much of the detailed removal-work data was missing.
  • Most workers used positive pressure masks, leaving few cases in the other respirator categories. Workers may have over-reported their use of respiratory protection, which could hide real differences.
  • The lack of a difference between wet and dry methods may reflect suppression technique combined with other working practices aimed at reducing exposure.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Relative Risk, Respirator, Lung Cancer, Mesothelioma, Asbestos Exposure.

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