Radiological changes in asbestos cement workers

Our plain-English summary of Radiological changes in asbestos cement workers, by K. Jakobsson, U. Strömberg, M. Albin, et al (Occupational and Environmental Medicine, 1995).

The study

• Authors: K. Jakobsson, U. Strömberg, M. Albin, H. Welinder, L. Hagmar
• Journal: Occupational and Environmental Medicine
• Published: 1995;52(1):20-7
• Cited by: 30 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objective: To explore associations between exposure to asbestos cement dust and radiographic findings in lung parenchyma and pleura.

Methods: Radiographs from 174 blue collar workers and 29 white collar workers from an asbestos cement plant formed one part of the study. Progression of small opacities was further studied in those 124 blue collar workers, for whom two radiographs taken after the end of employment were available. The median readings from five readers who used the full ILO 1980 classification were used. As exposure indices, time since start of employment, duration of employment, cumulative exposure, and average intensity of asbestos exposure were used. The influence of age and smoking was also considered in multiple logistic regression analyses.

Results: Small opacities (profusion > or = 1/0) were closely correlated with time related exposure variables, and showed weaker association with intensity based exposure variables. The odds ratio (OR) for small opacities was equal to 2.8 (90% CI 1.2, 6.7) in the > 30 f(fibre)-y/ml group, compared with those in the 0-10 f-y/ml group. Progression of at least two minor ILO categories after the end of employment was seen in 20%. Also, pleural thickening was closely related to time. By contrast, costophrenic angle obliterations were not associated with the time related variables, but closely associated with the intensity of asbestos exposure, and tended to occur during employment. The OR was 4.5 (90% CI 1.3, 15) in the > 2 f/ml group, compared with those in the 0-1 f/ml group.

Conclusions: In these workers, exposed mainly to chrysotile but also to small amounts of amphibole, the risk of radiographically visible parenchymal abnormality was substantially increased and strongly dependent on time related exposure variables. Progression was found long after the end of exposure. The findings on costophrenic angle obliterations, supposed to be sequelae of benign pleural effusions, were consistent with an immediate reaction triggered by intense asbestos exposure.

In plain English

This Swedish study examined chest X-rays of men from an asbestos cement plant using mainly chrysotile (over 95%), with some crocidolite and amosite before 1966. Five readers classified films by the 1980 ILO system. First available X-rays of 174 blue collar and 29 white collar workers were analysed. 124 blue collar men with two X-rays after leaving work were followed for progression. On first X-rays, 20% of blue collar workers had small opacities (lung-tissue changes) of profusion 1/0 or above. Above 30 fibre-years/ml the odds ratio was 2.8 (90% confidence interval 1.2 to 6.7), compared with under 10. For these first-X-ray findings, time-related measures showed the clearest links, while average intensity showed none. After leaving work, 24 of 124 men (20%) progressed at least two minor ILO profusion categories, more often with higher intensity and longer employment. Costophrenic angle obliteration, seen in 8% of blue collar workers, was also linked to intensity: odds ratio 4.5 (90% CI 1.3 to 15) above 2 fibres/ml versus under 1. The authors concluded that progression occurred long after exposure ended. Only survivors were studied.

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: Prevalence (cross-sectional) analysis of each worker's first available chest radiograph after the start of employment, plus a follow-up study of progression of small opacities between two radiographs taken after the end of employment. Five readers read the films independently using the ILO 1980 classification, and median readings were used.
• Who was studied: The study base was 249 male blue collar workers with at least 10 years of employment at an asbestos cement plant in the catchment area of Lund University Hospital, Sweden. They were born in 1900 or later and alive on 1 January 1978. Radiographs were found for 174 of these men. Radiographs from 29 white collar workers examined in 1978 were also included. The follow-up study covered 124 blue collar workers with at least two radiographs after the end of employment.
• Exposure: Asbestos cement dust at a plant that operated from 1907 to 1977. The asbestos was mainly chrysotile (more than 95%), with small amounts of crocidolite and amosite used before 1966. Exposure was measured as time since start of employment, duration of employment, cumulative exposure (fibre-years/ml) and average intensity (fibres/ml). The median cumulative exposure among blue collar workers was 19 f-y/ml (25th and 75th percentiles 8.6 and 47).
• Main results:
  • On the first available radiograph, 20% of the blue collar workers had small opacities of profusion 1/0 or above. The figure was 7% among white collar workers, but the authors stated that this cannot be directly compared because age and smoking differed between the groups.
  • Small opacities, adjusted for age and smoking, by cumulative exposure: OR 2.8 (90% CI 1.2, 6.7) in the group above 30 f-y/ml, compared with the 0 to 10 f-y/ml group.
  • Small opacities by time since start of employment: OR 7.3 (90% CI 1.9 to 29) in the group above 30 years, compared with the group below 15 years.
  • Average intensity of exposure did not influence the probability of small opacities of profusion 1/0 or above on the first radiograph.
  • After the end of employment, 24 of 124 blue collar workers (20%) showed progression of at least two minor ILO categories of profusion. The probability of progression increased with average intensity and with duration of employment.
  • Small opacities of profusion 1/0 or above were found in 40% of the last radiographs in the follow-up group, a median of 31 years after the start of employment.
  • Any chest wall (pleural) thickening was seen on the first radiograph in 48% of blue collar workers and 17% of white collar workers. Definite chest wall thickening was associated with each time-related exposure variable after adjustment for age.
  • Any diffuse chest wall thickening showed weak or no relations with the exposure variables examined.
  • Obliteration of the costophrenic angle was seen in 8% (14) of blue collar workers and in none of the white collar workers. It was not associated with duration of employment or time since start of employment.
  • Costophrenic angle obliteration by average intensity: OR 4.5 (90% CI 1.3 to 15) in the group above 2 f/ml and OR 2.1 (90% CI 0.68 to 6.2) in the intermediate group, both compared with the group below 1 f/ml.
  • Among men under 65, obliterations were found in nine men during employment and in one man out of 45 after the end of employment. The difference was not statistically significant (two-sided P = 0.28). The denominator for the during-employment group is damaged in the scan.
  • Among the 14 workers with obliterated costophrenic angles, one case of malignant mesothelioma was diagnosed 15 years after the obliteration appeared. The authors assumed that all obliterations represented benign effusions.
• The authors' conclusion: The authors concluded that in these workers, exposed mainly to chrysotile but also to small amounts of amphibole, the risk of radiographically visible parenchymal (lung tissue) abnormality was substantially increased and strongly dependent on time-related exposure variables, and that progression was found long after exposure ended. They considered the costophrenic angle findings, which they supposed to be after-effects of benign pleural effusions, consistent with an immediate reaction triggered by intense asbestos exposure.
• Limitations the authors state:
  • Only survivors were studied: men alive at the start of 1978, with few radiographs available for men who died in 1978 and 1979. The authors believed this tends to underestimate rather than overestimate the effects of exposure.
  • In the prevalence study the time of onset of an abnormality is not known. Time-related exposure measures may therefore be overestimated and average intensity underestimated.
  • The group of workers first employed after amphiboles were no longer used in production was too small to evaluate the effects of chrysotile exposure alone.
  • A posteroanterior chest radiograph cannot always distinguish circumscribed plaques from diffuse chest wall thickening.
  • A reduction of the hospital archives reduced the number of available radiographs.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Chrysotile, Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Asbestos-Cement, Parenchyma, Pleura, Cumulative Exposure, Asbestos Exposure, Odds Ratio, Pleural Thickening, Costophrenic angle.

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