Temporal Patterns of Exposure to Asbestos and Risk of Asbestosis: An Analysis of a Cohort of Asbestos Textile Workers

Our plain-English summary of Temporal Patterns of Exposure to Asbestos and Risk of Asbestosis: An Analysis of a Cohort of Asbestos Textile Workers, by A. Farioli, F.S. Violante, C. La Vecchia, et al (Journal of Occupational and Environmental Medicine, 2018).

The study

• Authors: A. Farioli, F.S. Violante, C. La Vecchia, E. Negri, C. Pelucchi, G. Spatari, P. Boffetta, E. Pira
• Journal: Journal of Occupational and Environmental Medicine
• Published: 2018;60(6):536-541
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objective: The aim of the study was to assess the risk of asbestosis death based on the temporal pattern of exposure to asbestos.

Methods: We followed up a cohort of asbestos textile workers, employed in 1946 to 1984, until November 2013. We measured the duration of the employment, the time since last employment (TSLE), the age, and the year of first employment. Hazard ratios (HR) were estimated through multivariable Cox regression models.

Results: We observed 51 asbestosis deaths among 1823 workers. The HR of asbestosis death increased with exposure duration (HR 2.4 for ≥15 years compared with <5 years, P trend = 0.014) and declined with TSLE (HR 0.3 for ≥25 compared with <5 years, P = 0.004). The risk of asbestosis mortality strongly declined for exposure starting after 1968.

Conclusions: The risk of asbestosis death strongly declines in the decades after cessation of the exposure.

In plain English

This study followed workers from an asbestos textile factory in Northern Italy to see how the timing of their asbestos exposure related to death from asbestosis. Various types of asbestos, including crocidolite, were used at the factory. Of 1,977 people employed there between 1946 and 1984, the authors analysed 1,823. They excluded people with earlier asbestos jobs or an unknown cause of death, and followed the rest to November 2013, up to age 85. Individual exposure levels were not available, so exposure was measured by length of employment. There were 51 asbestosis deaths, which was 5.6% of the 906 deaths before age 85. After adjustment, workers employed 15 years or more had a hazard ratio of 3.2 (95% CI 1.3–7.6) compared with those employed under 5 years. Risk was lower 25 or more years after leaving work (hazard ratio 0.3, 95% CI 0.1–0.9, versus under 5 years), although 13 of the 51 deaths occurred that late. Workers first hired from 1969 onward had lower risk. Workers first hired at age 35 or older had higher risk. The authors concluded that risk in the decades after exposure ended could be smaller than ecological studies suggested. Causes of death came only from official death records.

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 (historical) cohort mortality study analysed with Cox proportional hazards regression models
• Who was studied: All 1,977 workers (1,083 women and 894 men) employed at an asbestos textile factory in Northern Italy between 1946 and 1984, when the factory closed. After excluding 120 workers with previous employment in another asbestos factory and 34 deceased with unknown cause of death, 1,823 were analysed. Follow-up ran from January 1, 1946 to November 30, 2013 and was stopped at age 85.
• Exposure: Work in an asbestos textile factory that used various types of asbestos, including crocidolite. Measured fiber levels in the late 1960s were up to 100 fibers per ml in the opening and carding areas and 10–15 fibers per ml in spinning. Average levels in 1977 were 2 fibers per ml or less in all departments. Individual exposure was represented by duration of employment, time since last employment, and year and age at first employment.
• Main results:
  • Asbestosis was the underlying cause of 51 of the 906 deaths before age 85 (5.6%).
  • The overall crude asbestosis mortality rate in the cohort was 74 per 100,000 person-years (95% CI 56–97).
  • Risk rose with duration of employment. For 15 years or more versus under 5 years, the hazard ratio fell from 8.5 (crude) to 3.2 (95% CI 1.3–7.6) after adjustment for year of first exposure, time since last employment and sex. Adjusted hazard ratios were 2.5 (1.1–5.8) for 5–9 years and 4.2 (1.8–9.9) for 10–14 years.
  • Risk declined with time since last employment. The lowest adjusted hazard ratio was 0.3 (95% CI 0.1–0.9) for 25 years or more, compared with under 5 years.
  • Despite the decline, 13 of the 51 asbestosis deaths occurred 25 or more years after employment ended.
  • Workers first employed after 1968 had a hazard ratio of 0.3 (95% CI 0.1–0.8) compared with those first employed in 1960 or earlier.
  • Workers aged 35 or more at first employment had a hazard ratio of 2.7 (95% CI 1.1–6.4) compared with those under 25.
  • Men had a higher risk than women only when the timing of exposure was not taken into account. The adjusted hazard ratio for men was 1.2 (95% CI 0.7–2.2).
  • Sensitivity analyses gave estimates consistent with the main results. One extended the case definition to other pneumoconioses; the other used competing-risk models.
• The authors' conclusion: The authors concluded that the risk of asbestosis death in the decades after exposure ends could be smaller than generally thought based on ecological studies. They also concluded that the timing of exposure should always be assessed when investigating individual asbestosis risk.
• Limitations the authors state:
  • No individual data on exposure intensity were available. Calendar period was used as a stand-in for intensity.
  • Only deaths could be studied, not new cases of disease.
  • Diagnoses could not be checked, because only official death records were available.
  • Some deaths recorded as asbestosis may have been due to other forms of pulmonary fibrosis. Smoking history was not available.
  • Some workers may have left the factory because symptoms had begun. This could partly explain the higher risk soon after leaving.
  • Complete occupational histories were not available, so other asbestos exposure before or after this job could not be ruled out.
  • Asbestosis may have been underreported, particularly when the disease was mild.
  • Job titles and tasks were not available.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis.

Medical terms in this study, explained in our Lexicon: Hazard Ratio.

Related studies

• Validation of the diagnosis of mesothelioma and BAP1 protein expression in a cohort of asbestos textile workers from Northern Italy — P. Boffetta, L. Righi, et al. (2018)
• Cancer mortality in a cohort of asbestos textile workers — E. Pira, C. Pelucchi, et al. (2005)
• Updated mortality study of a cohort of asbestos textile workers — E. Pira, C. Romano, et al. (2016)
• Follow-up study of chrysotile asbestos textile workers: cohort mortality and case-control analyses — J.M. Dement, D.P. Brown, et al. (1994)
• Lung cancer mortality in North Carolina and South Carolina chrysotile asbestos textile workers — L. Elliott, D. Loomis, et al. (2012)
• An updated historical cohort mortality study of workers exposed to asbestos in a refitting shipyard, 1947-2007 — K. Tomioka, Y. Natori, et al. (2011)

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