Occupational exposures and idiopathic pulmonary fibrosis

Our plain-English summary of Occupational exposures and idiopathic pulmonary fibrosis, by G.I. Walters (Current Opinion in Allergy and Clinical Immunology, 2020).

The study

• Author: G.I. Walters
• Journal: Current Opinion in Allergy and Clinical Immunology
• Published: 2020;20(2):103-111
• Type of article: Review
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Purpose Of Review: A recent meta-analysis of data from international case-control studies reports a population attributable fraction of 16% for occupational factors in the cause of idiopathic pulmonary fibrosis (IPF). Smoking, genetic factors and other prevalent diseases only partly explain IPF, and so this review aims to summarize recent progress in establishing which occupational exposures are important in cause.

Recent Findings: IPF is a rare disease, although it is the commonest idiopathic interstitial pneumonia. Epidemiological study suggests that incidence of IPF is increasing, particularly in older men. There are significant associations with IPF and occupational exposures to organic dust, including livestock, birds and animal feed, metal dust, wood dust and silica/minerals. Estimates of effect vary between studies, and are influenced by the distribution of employment, study design and case definition. Inhalation of asbestos fibres is a known cause of usual interstitial pneumonia (as seen histologically in IPF), though there are significant linear relationships between asbestos consumption, and mortality from both IPF and mesothelioma, leading to the hypothesis that low-level asbestos exposure may cause IPF.

Summary: Research must focus on exposure-response relationships between asbestos and other occupational inhaled hazards, and IPF. Funding bodies and policy makers should acknowledge the significant occupational burden on IPF.

In plain English

This review summarized published research on occupational exposures and idiopathic pulmonary fibrosis (IPF), a progressive scarring (fibrotic) lung disease of apparently unknown cause. The author described case–control studies from several countries reporting associations between IPF and metal dust, wood dust, organic dust, and silica or minerals. A 2019 meta-analysis of 11 such studies, by Blanc and colleagues, found statistically significant pooled associations for every exposure category except agricultural dust. On asbestos, the author reported that a UK study by Barber and colleagues found asbestos consumption correlated significantly with IPF deaths (r = 0.92 in males and 0.93 in females). A study of 31 European countries by the same group, presented as a conference abstract, found age-standardized IPF mortality correlated with mesothelioma mortality (r = 0.52). Interim data from a UK case–control study suggested that 65% of enrolled hospital-diagnosed IPF cases had high-level or medium-level occupational asbestos exposure. The author concluded that metal, wood, organic and silica/mineral dusts contribute to the cause of IPF. The author also concluded that an association with low-level or hidden asbestos exposure is not yet established and requires further research.

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: Narrative review of published studies (mainly case–control and mortality studies) on occupational exposures and IPF; no new data were collected
• Who was studied: Published studies, not patients directly: 14 case–control studies tabulated from the United Kingdom, Japan, United States, Sweden, Mexico, Egypt, Italy and Korea, a 2019 meta-analysis, and UK and European mortality studies on asbestos and IPF
• Exposure: Occupational inhaled exposures: metal dust, wood dust, organic (agricultural) dust including livestock, birds and animal feed, silica/minerals, and asbestos (the UK mortality study used imports of chrysotile, amosite and crocidolite)
• Main results:
  • In the 2019 meta-analysis by Blanc et al. of 11 case–control studies or study components, all exposure categories except agricultural dust had statistically significant pooled associations with IPF. Pooled odds ratios were: vapours/gases/dusts/fumes combined 2.0 (95% CI 1.2 to 3.2; population attributable fraction 26, 95% CI 10 to 41); metal dust 2.0 (95% CI 1.3 to 3.0; attributable fraction 8); wood dust 1.7 (95% CI 1.3 to 2.2; attributable fraction 4); silica dust 1.7 (95% CI 1.2 to 2.4; attributable fraction 3).
  • Across the reviewed case–control studies, odds ratios for metal exposure were at least two in six studies (range 1.7 to 11).
  • In the UK study by Barber et al. covering 1962 to 2012, asbestos consumption correlated significantly with IPF deaths (r = 0.92 in males, r = 0.93 in females, both P less than 0.001) and with mesothelioma deaths (r = 0.91 in males, r = 0.87 in females, both P less than 0.001).
  • In a study of 31 European countries by Barber et al., presented as a conference abstract, age-standardized IPF mortality (but not mortality from other interstitial lung diseases) was significantly associated with mesothelioma mortality (r = 0.52, P = 0.003) and with per capita asbestos consumption (r = 0.37, P = 0.046).
  • Interim data from the UK IPF-JES case–control study suggested that 65% of enrolled hospital-diagnosed IPF cases had had high-level or medium-level occupational asbestos exposure, for a mean duration of 24 years. Final results were awaited.
  • In a 2013 case-cohort study cited by the author, 20 of 46 patients with an initial guideline-based diagnosis of IPF were later diagnosed with hypersensitivity pneumonitis.
• The authors' conclusion: The author concluded that occupational exposure to metal dust, wood dust, organic dust and silica/mineral dust contributes to the cause of IPF and makes up a significant portion of the disease burden. The author also concluded that an association between IPF and low-level or hidden asbestos exposure is not yet established and requires further research.
• Limitations the authors state:
  • Effect estimates varied between studies and were likely influenced by the distribution of employment in each country, study methods and how IPF cases were defined.
  • In many of the studies in the meta-analysis, occupational exposures were self-reported, which raises the possibility of recall bias.
  • Some cases or exposures may have been misclassified, for example chronic hypersensitivity pneumonitis counted as IPF, or wood dust exposure with unrecognized asbestos exposure.
  • Asbestos exposure had not been strongly associated with IPF in previous case–control studies.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Idiopathic, Pulmonary Fibrosis, Meta-Analysis, Population Attributable Fraction (PAF), Interstitial, Mesothelioma, Asbestos Exposure.

Related studies

• The Role of Occupational and Environmental Exposures in the Pathogenesis of Idiopathic Pulmonary Fibrosis: A Narrative Literature Review — S.P. Trethewey, G.I. Walters (2018)
• Smoking, occupational exposures, and idiopathic pulmonary fibrosis among Swedish construction workers — M. Andersson, P.D. Blanc, et al. (2021)
• Occupational and environmental risk factors for idiopathic pulmonary fibrosis in Australia: case-control study — M.J. Abramson, T. Murambadoro, et al. (2020)
• Antifibrotic treatment response and prognostic predictors in patients with idiopathic pulmonary fibrosis and exposed to occupational dust — V. Casillo, S. Cerri, et al. (2019)
• What role for asbestos in idiopathic pulmonary fibrosis? Findings from the IPF job exposures case-control study — C.J. Reynolds, R. Sisodia, et al. (2023)
• UK asbestos imports and mortality due to idiopathic pulmonary fibrosis — C.M. Barber, R.E. Wiggans, et al. (2016)

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