Occupational and environmental risk factors for idiopathic pulmonary fibrosis in Australia: case-control study

Our plain-English summary of Occupational and environmental risk factors for idiopathic pulmonary fibrosis in Australia: case-control study, by M.J. Abramson, T. Murambadoro, S.M. Alif, et al (Thorax, 2020).

The study

• Authors: M.J. Abramson, T. Murambadoro, S.M. Alif, G.P. Benke, S.C. Dharmage, I. Glaspole, P. Hopkins, R.F. Hoy, S. Klebe, Y. Moodley, S. Rawson, P.N. Reynolds, R. Wolfe, T.J. Corte, E.H. Walters, Australian IPF Registry
• Journal: Thorax
• Published: 2020;75(10):864-869
• Cited by: 68 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Introduction: Idiopathic pulmonary fibrosis (IPF) is a lung disease of unknown cause characterised by progressive scarring, with limited effective treatment and a median survival of only 2-3 years. Our aim was to identify potential occupational and environmental exposures associated with IPF in Australia.

Methods: Cases were recruited by the Australian IPF registry. Population-based controls were recruited by random digit dialling, frequency matched on age, sex and state. Participants completed a questionnaire on demographics, smoking, family history, environmental and occupational exposures. Occupational exposure assessment was undertaken with the Finnish Job Exposure Matrix and Australian asbestos JEM. Multivariable logistic regression was used to describe associations with IPF as ORs and 95% CIs, adjusted for age, sex, state and smoking.

Results: We recruited 503 cases (mean±SD age 71±9 years, 69% male) and 902 controls (71±8 years, 69% male). Ever smoking tobacco was associated with increased risk of IPF: OR 2.20 (95% CI 1.74 to 2.79), but ever using marijuana with reduced risk after adjusting for tobacco: 0.51 (0.33 to 0.78). A family history of pulmonary fibrosis was associated with 12.6-fold (6.52 to 24.2) increased risk of IPF. Occupational exposures to secondhand smoke (OR 2.1; 1.2 to 3.7), respirable dust (OR 1.38; 1.04 to 1.82) and asbestos (OR 1.57; 1.15 to 2.15) were independently associated with increased risk of IPF. However occupational exposures to other specific organic, mineral or metal dusts were not associated with IPF.

Conclusion: The burden of IPF could be reduced by intensified tobacco control, occupational dust control measures and elimination of asbestos at work.

© Author(s) (or their employer(s)) 2020. No commercial re-use. See rights and permissions. Published by BMJ.

In plain English

This case-control study compared 503 Australians with idiopathic pulmonary fibrosis (IPF), a scarring lung disease, from the Australian IPF Registry with 902 population controls of similar age, sex and state. Workplace exposures were estimated from job histories using a Finnish job exposure matrix (FinJEM) and an Australian asbestos matrix (AsbJEM). Self-reported workplace asbestos exposure was associated with IPF (odds ratio 1.37, 95% CI 1.08 to 1.74). Using AsbJEM, the odds rose with cumulative asbestos exposure, reaching 1.57 (1.15 to 2.15) in the highest quartile versus the lowest. Asbestos assessed by FinJEM was not significantly associated (1.31, 0.84 to 2.07). The authors gave more weight to the AsbJEM results. Workplace secondhand smoke (2.10, 1.20 to 3.70), respirable dust (1.38, 1.04 to 1.82), ever smoking tobacco (2.20, 1.74 to 2.79) and a family history of pulmonary fibrosis (12.6, 6.52 to 24.2) were associated with IPF. The authors attributed an estimated 0.8% of IPF to asbestos. They suspected some cases diagnosed as IPF may be unrecognised asbestosis. They concluded that tobacco control, dust control and eliminating asbestos at work could reduce the burden of IPF.

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: Case-control study
• Who was studied: 503 people with IPF (cases) from the Australian IPF Registry, a national registry set up in 2012, with diagnoses confirmed by multidisciplinary review. They were compared with 902 population-based controls recruited by random digit dialling and frequency matched 2:1 on age, sex and state of residence. Cases had an average age of 71.1 years and 69% were male; controls had an average age of 70.8 years and 69% were male. Recruitment dates are not stated.
• Exposure: Smoking, family history, home exposures and self-reported workplace exposures (including asbestos and silica). Occupational exposures were also coded from job histories with the Finnish Job Exposure Matrix (FinJEM). Asbestos was additionally estimated with the Australian asbestos JEM (AsbJEM) as cumulative fibre-years/mL, grouped into quartiles. Fiber types are not specified.
• Main results:
  • Self-reported workplace asbestos exposure: 194 of 484 cases (40.1%) and 304 of 902 controls (33.7%). Adjusted OR 1.37 (95% CI 1.08 to 1.74).
  • Asbestos assessed by AsbJEM, compared with the lowest quartile: adjusted OR 1.21 (0.88 to 1.66) in the second quartile, 1.41 (1.03 to 1.93) in the third and 1.57 (1.15 to 2.15) in the fourth. With additional adjustment for pack-years, the fourth-quartile OR was 1.61 (1.14 to 2.27).
  • Asbestos assessed by FinJEM was not significantly associated with IPF: 38 of 397 cases (9.6%) and 54 of 744 controls (7.3%) were exposed. Adjusted OR 1.31 (0.84 to 2.07), p=0.236.
  • The authors gave more weight to the AsbJEM findings, which they considered consistent with a dose response relationship to asbestos.
  • Occupational exposures assessed by FinJEM: secondhand smoke at work was found in 42 of 85 cases (49.4%) and 59 of 203 controls (29.1%), adjusted OR 2.10 (1.20 to 3.70). Respirable dust: adjusted OR 1.38 (1.04 to 1.82).
  • Ever smoking tobacco: adjusted OR 2.20 (1.74 to 2.79).
  • Family history of pulmonary fibrosis: 63 of 490 cases (12.9%) and 11 of 902 controls (1.2%). Adjusted OR 12.6 (6.52 to 24.2).
  • Estimated population attributable fractions: 11.6% of IPF to secondhand smoke, 7.6% to respirable dust and 0.8% to asbestos.
• The authors' conclusion: The authors concluded that the burden of IPF could be reduced by intensified tobacco control, occupational dust control measures and elimination of asbestos at work.
• Limitations the authors state:
  • Some selection bias was likely because registration in the registry was voluntary.
  • Residual confounding by unmeasured factors such as socioeconomic status remained possible.
  • Some exposures and family history were self-reported and subject to recall bias.
  • Cases completed paper questionnaires while controls were interviewed by telephone, which could have introduced bias.
  • Some associations may have been chance findings because many comparisons were made.
  • The authors note that self-reported asbestos exposure is generally considered less accurate than exposure assessed by a job exposure matrix.
  • The authors suspected that some cases called IPF are actually unrecognised asbestosis.
  • The attributable fraction estimates are uncertain because it is not accurately known how many workers are exposed to respirable dust.

Topics

Medical terms in this study, explained in our Lexicon: Idiopathic, Pulmonary Fibrosis, Case-Control Study, Median Survival, Environmental Exposure, Occupational Exposure, Dust Control.

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