The natural history of asbestosis in former crocidolite workers of Wittenoom Gorge

Our plain-English summary of The natural history of asbestosis in former crocidolite workers of Wittenoom Gorge, by W. Cookson, N. De Klerk, A.W. Musk, et al (The American Review of Respiratory Disease, 1986).

The study

• Authors: W. Cookson, N. De Klerk, A.W. Musk, J.J. Glancy, B. Armstrong, M. Hobbs
• Journal: The American Review of Respiratory Disease
• Published: 1986;133(6):994-8
• Cited by: 46 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000385).

Abstract

The course of pulmonary asbestosis and its determinants have been examined in 280 applicants for compensation among former workers of the crocidolite mine and mill at Wittenoom Gorge, Western Australia. Serial chest radiographs accrued over more than 3 decades were graded for parenchymal disease separately by two observers according to the 1980 ILO Classification of Radiographs for Pneumoconioses and without knowledge of exposure histories or compensation details. In 136 subjects whose median duration of exposure was 37 months, radiographic asbestosis appeared between 1 and 34 yr after initial exposure and then progressed continuously. Total exposure to asbestos and time from first exposure to the appearance of definite radiographic asbestosis were significant determinants of the rate of progression of profusion of radiographic abnormality. Asbestosis should be considered to be an active disease even 3 decades after exposure has ended.

In plain English

This retrospective study followed asbestosis on X-rays in former crocidolite mine and mill workers at Wittenoom, Western Australia. X-rays were found for 280 of 354 men seeking asbestosis compensation between 1947 and 1983; 136 qualified by one reader and 139 by another. Readers graded films by the 1980 ILO classification, blind to exposure and compensation. For the first reader, asbestosis appeared 2 to 34 years after starting work (median 14), then kept progressing. No improvement was seen, though the authors noted their reading method was poorly suited to detecting it. Men exposed above 148 fibers per cubic centimeter per year moved from ILO Category 1 to 2 at 2.5 times the rate (95% confidence interval 1.2 to 5.4) of men below 55. Men reaching Category 1 within 9 years of first exposure made that move at 8.0 times the rate (2.9 to 21.7) of those taking 20 years or more. The authors found no evidence exposure affected when asbestosis first appeared; smoking could not be analyzed. The authors concluded the X-ray changes are continuously progressive, at least in crocidolite workers.

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 study of serial chest radiographs (natural history study) among compensation applicants from a worker cohort, analyzed with an extension of the Cox proportional hazards model
• Who was studied: 354 former Wittenoom crocidolite workers who applied to the Pneumoconiosis Medical Board of Western Australia for asbestosis compensation between 1947 and 1983. Radiographs were recovered for 280 men. After exclusions, 136 (Reader 1) and 139 (Reader 2) had definite radiographic pneumoconiosis and were included. They came from a cohort of over 6,000 former workers; the mine operated from 1943 to 1966.
• Exposure: Exclusively crocidolite, from mining and milling at Wittenoom. Cumulative exposure in fibers per cubic centimeter per year was estimated from work histories and 1966 fiber counts. The median cumulative exposure was 91 fibers per cubic centimeter per year and the median duration of exposure was 37 months (Reader 1).
• Main results:
  • The two readers agreed well on the profusion of the last film for all 280 men (Kendall's tau B 0.71). Reader 2 tended to score 1 or 2 minor ILO categories higher.
  • Reader 1: onset of definite radiographic asbestosis was seen 2 to 34 years after starting work (median 14 years). No one developed asbestosis while still employed.
  • Reader 2: onset 1 to 33 years after starting work (median 13 years). Asbestosis was diagnosed in 7 men while still at work. Later analyses were similar for both readers, so only Reader 1's results were presented.
  • Progression from Category 1 to Category 2, compared with exposure below 55 fibers per cubic centimeter per year: relative rate 2.5 (95% CI 1.2 to 5.4) for exposure above 148, and 1.6 (1.1 to 2.3) for 55 to 148. For progression from Category 2 to Category 3, the exposure effect could have been due to chance (p = 0.08).
  • Progression from Category 1 to Category 2, compared with men taking 20 years or more to reach Category 1: relative rate 8.0 (95% CI 2.9 to 21.7) for men reaching Category 1 within 0 to 9 years of first exposure, and 2.8 (1.7 to 4.7) for 10 to 19 years. There was no evidence of a similar effect on progression from Category 2 to Category 3.
  • There was no evidence of an effect of cumulative exposure on the time to onset of pneumoconiosis in these data. Progression of established asbestosis did depend on exposure.
  • A weak effect of age at first exposure on all transitions was significant overall (p = 0.05). The authors said it most likely reflects current age.
  • No radiographic improvement was observed. In only 6 of the 136 subjects was no progression of one minor category or more seen in the last 10 years of follow-up.
• The authors' conclusion: The authors concluded that the radiographic changes of asbestosis are continuously progressive, at least in workers exposed to crocidolite. They found that the rate of progression of established asbestosis increases with accumulated exposure and decreases with longer time from first exposure to onset.
• Limitations the authors state:
  • Smoking data were too limited to analyze, and more than 80% of subjects were known smokers.
  • Fiber counts were estimated from measurements taken late in the life of the mine and mill, so the absolute exposure values are considered conservative.
  • The side-by-side film reading method was not the best suited to detecting radiographic improvement.
  • Few men were in Category 2 early on, so an apparent effect on progression from Category 2 to Category 3 was not statistically significant.

Mines named here

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

• Wittenoom, Western Australia

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Crocidolite, Wittenoom, Asbestosis, Chest X-Ray, ILO Classification.

Related studies

• Comparison of measures of exposure to asbestos in former crocidolite workers from Wittenoom Gorge, W. Australia — N.H. de Klerk, A.W. Musk, et al. (1996)
• Prevalence of radiographic asbestosis in crocidolite miners and millers at Wittenoom, Western Australia — W.O. Cookson, N.H. De Klerk, et al. (1986)
• Morphology of bronchogenic carcinoma in workers formerly exposed to crocidolite at Wittenoom Gorge in Western Australia — J.E. Baker, D.C. Reutens, et al. (1986)
• Benign and malignant pleural effusions in former Wittenoom crocidolite millers and miners — W.O. Cookson, N.H. De Klerk, et al. (1985)
• Prediction of mesothelioma, lung cancer, and asbestosis in former Wittenoom asbestos workers — G. Berry (1991)
• Malignant pleural and peritoneal mesotheliomas in former miners and millers of crocidolite at Wittenoom, Western Australia — G. Berry, N.H. de Klerk, et al. (2004)

Browse more research in The American Review of Respiratory Disease, or return to medical research.