Screening of miners and millers at decreasing levels of asbestos exposure: comparison of chest radiography and thin-section computed tomography

Our plain-English summary of Screening of miners and millers at decreasing levels of asbestos exposure: comparison of chest radiography and thin-section computed tomography, by M. Terra-Filho, E. Bagatin, L.E. Nery, et al (PloS One, 2015).

The study

• Authors: M. Terra-Filho, E. Bagatin, L.E. Nery, L.M. Nápolis, J.A. Neder, G.S. Meirelles, C.I. Silva, N.L. Muller
• Journal: PloS One
• Published: 2015;10(3):e0118585
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Chest radiography (CXR) is inferior to Thin-section computed tomography in the detection of asbestos related interstitial and pleural abnormalities. It remains unclear, however, whether these limitations are large enough to impair CXR´s ability in detecting the expected reduction in the frequency of these asbestos-related abnormalities (ARA) as exposure decreases.

Methods: Clinical evaluation, CXR, Thin-section CT and spirometry were obtained in 1418 miners and millers who were exposed to progressively lower airborne concentrations of asbestos. They were separated into four groups according to the type, period and measurements of exposure and/or procedures for controlling exposure: Group I (1940-1966/tremolite and chrysotile, without measurements of exposure and procedures for controlling exposure); Group II (1967-1976/chrysotile only, without measurements of exposure and procedures for controlling exposure); Group III (1977-1980/chrysotile only, initiated measurements of exposure and procedures for controlling exposure) and Group IV (after 1981/chrysotile only, implemented measurements of exposure and a comprehensive procedures for controlling exposure).

Results: In all groups, CXR suggested more frequently interstitial abnormalities and less frequently pleural plaques than observed on Thin-section CT (p<0.050). The odds for asbestosis in groups of decreasing exposure diminished to greater extent at Thin-section CT than on CXR. Lung function was reduced in subjects who had pleural plaques evident only on Thin-section CT (p<0.050). In a longitudinal evaluation of 301 subjects without interstitial and pleural abnormalities on CXR and Thin-section CT in a previous evaluation, only Thin-section CT indicated that these ARA reduced as exposure decreased.

Conclusions: CXR compared to Thin-section CT was associated with false-positives for interstitial abnormalities and false-negatives for pleural plaques, regardless of the intensity of asbestos exposure. Also, CXR led to a substantial misinformation of the effects of the progressively lower asbestos concentrations in the occurrence of asbestos-related diseases in miners and millers.

In plain English

This Brazilian cross-sectional study compared chest X-rays with thin-section CT in 1418 workers and ex-workers of one asbestos mining and milling company. Workers formed four groups of decreasing exposure, from Group I (1940 to 1966, chrysotile with tremolite, no controls) to Group IV (from 1981, chrysotile only, full controls). Mean cumulative exposure fell from 110.9 fibres-cc-years (Group I) to 3.6 (Group IV). In every group, X-rays suggested interstitial abnormalities more often, and pleural plaques less often, than CT. In Group I, CT found plaques in 60 of 123 workers (48.8%), X-ray in 10 (8.1%). In Groups II and III, workers with plaques only on CT had lower lung function than workers normal on both tests. Among 301 workers free of abnormalities on both tests in 1997 to 2000 and rechecked in 2007 to 2010, only CT showed the rate of new cases falling as exposure decreased. The authors concluded that, compared with CT, X-rays gave false positives for interstitial abnormalities and false negatives for plaques, and that CT should be considered for following workers exposed to low doses.

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: Cross-sectional study comparing chest radiography with thin-section CT, with a longitudinal analysis of a subgroup
• Who was studied: 1418 workers and ex-workers of one asbestos mining and milling company in Brazil (SAMA), in four exposure groups: Group I (n = 123, 1940 to 1966, São Félix mine, Bahia, where tremolite was found with chrysotile), Group II (n = 600, 1967 to 1976), Group III (n = 479, 1977 to 1980) and Group IV (n = 216, from 1981), at the Canabrava mine, Goiás
• Exposure: Asbestos dust in mining and milling: chrysotile, plus tremolite in Group I. Mean cumulative exposure was 110.9 fibres-cc-years in Group I, 44.1 in Group II, 7.6 in Group III and 3.6 in Group IV.
• Main results:
  • In all four groups, chest X-ray suggested interstitial abnormalities more often and pleural plaques less often than thin-section CT (p less than 0.050).
  • In Group I, pleural plaques were seen on CT in 60 workers (48.8%) and on chest X-ray in 10 (8.1%). Interstitial abnormalities were seen on CT in 12 (9.8%) and on X-ray in 16 (13.0%).
  • Older age and cigarette smoking were associated with higher odds of interstitial abnormalities or pleural plaques. Workers in the later groups (II to IV) had lower odds than Group I.
  • In Groups II and III, workers with pleural plaques seen only on CT had consistently lower smoking-adjusted spirometry values than workers normal on both CT and X-ray.
  • The longitudinal subgroup was restricted to 301 workers with no abnormalities on either CT or chest X-ray at the first evaluation.
  • These 301 workers were first evaluated in 1997 to 2000 and re-examined by both methods in 2007 to 2010.
  • In the longitudinal subgroup, only thin-section CT indicated that incidence rates of asbestos-related disease went down as exposure decreased from Group I to Group IV.
  • In the longitudinal subgroup, CT showed 11 new asbestosis cases, all in Group I (3) and Group II (8). The incidence rate ratio for asbestosis on CT in Group II versus Group I was 0.24 (0.06 to 0.90).
  • In the longitudinal subgroup, CT showed 18 new pleural plaque cases. Compared with Group I, the incidence rate ratio was 0.20 (0.07 to 0.60) for Group II and 0.08 (0.02 to 0.36) for Group III.
  • Using chest X-ray in the longitudinal subgroup, the incidence rate ratios for asbestosis versus Group I were 1.08 (0.14 to 8.36), 0.76 (0.09 to 6.33) and 0.84 (0.05 to 13.49) for Groups II, III and IV. These did not show the decrease seen on CT.
• The authors' conclusion: The authors concluded that, compared with thin-section CT, chest X-ray gave false positives for interstitial abnormalities and false negatives for pleural plaques, and that thin-section CT should be considered instead of chest X-ray for the longitudinal evaluation of people exposed to low doses of asbestos fibres.
• Limitations the authors state:
  • Survival bias might have influenced the results, though the authors considered this unlikely to be serious in this sample with mild disease.
  • There was no tissue (histopathologic) proof of asbestosis.
  • The findings should not be extrapolated to groups with extensive lung or pleural abnormalities.
  • Cost-benefit and operational issues in choosing between the two methods were not addressed.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Cana Brava mine, Uruaçu, Goiás

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile, Tremolite.

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Interstitial, Spirometry, Tremolite, Chrysotile, Pleural Plaques.

Related studies

• Agreement between chest radiography and high-resolution computed tomography in diagnosing dust-related interstitial lung fibrosis — R.R. Tiwari (2015)
• Thin-section CT abnormalities and pulmonary gas exchange impairment in workers exposed to asbestos — A. Sette, J.A. Neder, et al. (2004)
• Fiber burden and patterns of asbestos-related disease in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1993)
• Mineralogic correlates of fibrosis in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1989)
• Non-malignant consequences of decreasing asbestos exposure in the Brazil chrysotile mines and mills — E. Bagatin, J.A. Neder, et al. (2005)
• Asbestos-related pleural disease and asbestosis: a comparison of CT and chest radiography — A.C. Friedman, S.B. Fiel, et al. (1988)

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