Pulmonary Function and CT Scan Imaging at Low-Level Occupational Exposureto Asbestos

Our plain-English summary of Pulmonary Function and CT Scan Imaging at Low-Level Occupational Exposureto Asbestos, by G. Satta, T. Serra, F. Meloni, et al (International Journal of Environmental Research and Public Health, 2019).

The study

• Authors: G. Satta, T. Serra, F. Meloni, A. Lazzarato, A. Argiolas, E. Bosu, A. Coratza, N. Frau, M. Lai, L.I. Lecca, N. Mascia, I. Pilia, V. Piras, G. Sferlazzo, M. Campagna, P. Cocco
• Journal: International Journal of Environmental Research and Public Health
• Published: 2019;17(1)
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: In spite of the reduced exposure level, and its ban in numerous countries, compensation claims for asbestos-related diseases are far from decreasing. Methods: We used retrospective exposure assessment techniques to explore respiratory function and a computerized tomography (CT) scan in relation to past asbestos exposure in 115 male workers retired from an acrylic and polyester fiber plant. Based, on detailed information on exposure circumstances, we reconstructed a cumulative exposure estimate for each patient. Results: Time-weighted average exposure in our study population was 0.24 fibers/ml (95% confidence inteval (CI) 0.19-0.29), and the average cumulative exposure was 4.51 fibers/mL-years (95% CI 3.95-5.07). Exposure was elevated among maintenance workers, compared to other jobs (p = 0.00001). Respiratory function parameters did not vary in relation to the exposure estimates, nor to CT scan results. Risk of interstitial fibrosis showed a significant upward trend (Wald test for trend = 2.62, p = 0.009) with cumulative exposure to asbestos; risk associated with 5.26 fibers/mL-years or more, was 8-fold (95% CI 1.18-54.5). Conclusions: Our results suggest that a CT scan can detect pleuro-parenchymal lung alterations at asbestos exposure levels lower than previously thought, in absence of respiratory impairment. Further studies are required to validate our techniques of retrospective assessment of asbestos exposure.

In plain English

The authors studied 115 retired male workers from an acrylic and polyester fiber plant in Sardinia, Italy, seen at a university occupational health clinic between February 2017 and July 2019. From each man's detailed job history and published databases of airborne asbestos measurements, they estimated past exposure. The article does not name the fiber type. Estimated exposure was relatively low, averaging 0.24 fibers/mL as a time-weighted average and 4.51 fibers/mL-years cumulatively, and was higher in maintenance workers. Lung function results were not related to the exposure estimates or to CT findings. Of 112 workers with a recent CT scan, 16 (14.3%) had interstitial fibrosis with or without pleural plaques (Gamsu grades II to VI). The odds of this finding rose with estimated cumulative exposure. In the top quarter (5.26 fibers/mL-years or more) the odds were 8.0 times those in the lowest quarter (95% CI 1.18 to 54.5). The authors concluded there was a strong association at exposure levels lower than previously considered. They called for validation of their exposure method and noted few cases, wide confidence intervals and self-selected participants.

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: Study of former asbestos-exposed workers attending a health screening clinic. Individual past exposure was reconstructed retrospectively from job histories and databases. CT findings were analysed with a case-control approach using logistic regression adjusted for age and smoking.
• Who was studied: 115 male workers formerly exposed to asbestos at an acrylic and polyester fiber plant in Sardinia, Italy. They attended the Occupational Health outpatient service at the University Hospital of Cagliari between February 2017 and July 2019. By job, there were 38 plant operators, 16 service workers and 61 maintenance workers. The mean age was 65.5 years. Three men without a recent CT scan were excluded from the CT analysis, leaving 112.
• Exposure: Occupational asbestos exposure at the plant, with no fiber type named. Direct exposure came from job tasks involving handling, cutting or abrading asbestos-containing materials, either friable or compact. Indirect exposure came from contamination of the work environment during maintenance. Time-weighted average and cumulative exposure (fibers/mL-years) were estimated from the Datamyant and Ev@lutil databases and published reports. Average duration of exposure was 18.7 years.
• Main results:
  • Whole study population: mean time-weighted average exposure was 0.24 f/mL (95% CI 0.19 to 0.30). Average cumulative exposure was 4.51 f/mL-years (95% CI 3.40 to 5.61).
  • Maintenance workers had higher estimated exposure (mean 0.36 f/mL, 95% CI 0.30 to 0.43) than plant operators and service workers (p = 0.00001).
  • Interstitial fibrosis with or without pleural plaques (Gamsu grades II to VI) was found in 16 of 112 workers (14.3%). The rate was 10 of 59 (16.9%) in maintenance workers and 6 of 53 (11.3%) in plant operators and service workers combined.
  • Lung function measures were not related to the CT results, or to time-weighted average or cumulative asbestos exposure, after adjusting for age and smoking.
  • The odds of Gamsu grade II to VI fibrosis showed significant upward trends with estimated time-weighted average exposure (p = 0.0045) and with cumulative exposure (p = 0.009).
  • Compared with the lowest quartile, the top quartile of cumulative exposure (5.26 f/mL-years or more) had OR 8.0 (95% CI 1.18 to 54.5) for Gamsu grade II to VI fibrosis. Cumulative exposure of 10 f/mL-years or more had OR 10.8 (95% CI 1.54 to 75.7).
  • Working 20 or more years as a maintenance worker was associated with OR 2.7 for Gamsu grade II to VI fibrosis. The 95% CI was 0.77 to 9.61, which includes 1. Maintenance work showed no increase in risk of lighter (Gamsu grade I) fibrosis.
  • The authors stated that the odds of interstitial fibrosis and/or pleural plaques were elevated at estimated exposure levels well below 25 f/mL-years.
• The authors' conclusion: The authors concluded that they observed a strong association between their estimates of airborne asbestos exposure and interstitial fibrosis of the lung, at levels lower than previously considered. They said further studies are needed to validate their retrospective exposure assessment techniques before these are used in health screening programs.
• Limitations the authors state:
  • The risk estimates were imprecise because there were few cases, and only one case fell in the reference (lowest) exposure quartile.
  • Participants were self-selected volunteers. If attendance was related to CT results, the prevalence of fibrosis could be inflated and the findings may not generalize.
  • The small study size limited statistical power to detect small effects of low-level asbestos exposure and smoking on lung function.
  • There was no unexposed comparison group, so the lowest exposure quartile served as the reference and a threshold could not be derived.
  • Mostly only written CT reports, not the images, were available, so the ICOERD classification could not be applied. The simpler Gamsu grading was used instead.
  • Exposure may have been underestimated; the authors said true levels might have been up to 4 times higher.

Topics

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

Medical terms in this study, explained in our Lexicon: CT Scan, Asbestos Exposure, Cumulative Exposure, Time-Weighted Average (TWA), Interstitial Fibrosis.

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