Prevalence of radiographic asbestosis in crocidolite miners and millers at Wittenoom, Western Australia

Our plain-English summary of Prevalence of radiographic asbestosis in crocidolite miners and millers at Wittenoom, Western Australia, by W.O. Cookson, N.H. De Klerk, A.W. Musk, et al (British Journal of Industrial Medicine, 1986).

The study

• Authors: W.O. Cookson, N.H. De Klerk, A.W. Musk, B.K. Armstrong, J.J. Glancy, M.S. Hobbs
• Journal: British Journal of Industrial Medicine
• Published: 1986;43(7):450-7
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001168).

Abstract

An estimate has been made of the prevalence of unrecognised pneumoconiosis in former crocidolite workers from Wittenoom, Western Australia. All plain chest radiographs relating to a one in six random sample (1025 men) of all former Wittenoom workers who had never entered a compensation claim to the Pneumoconiosis Medical Board of Western Australia were sought from Perth teaching hospitals and from the Perth Chest Clinic where compulsory examination of all workers in the mining industry takes place. Radiographs were recovered for 83% of the men and read independently by two observers. By means of logistic regression analysis a current prevalence of parenchymal abnormality (defined as a radiographic profusion of small opacities of category 1/0 or greater on the ILO classification) of nearly 20% was calculated after adjustment for age, time since first exposure, and cumulative exposure level. One hundred men randomly selected from those known to be alive in the sample were invited to attend for a new radiographic examination. Seventy four men attended and the predicted prevalence was confirmed. It is estimated from these data that there were between 450 and 900 former Wittenoom workers in Australia at the end of 1980 who had radiographic abnormality consistent with pneumoconiosis but had not claimed compensation or had asbestosis diagnosed. The data are consistent with there being no threshold dose of crocidolite exposure for the development of radiographic abnormality in this group.

In plain English

This study estimated how many former Wittenoom crocidolite workers had chest X-ray changes consistent with pneumoconiosis without having claimed compensation. Of a random one-in-six sample of 1025 such men, 541 had X-rays taken after starting work. Two readers graded films by the ILO system, counting small-opacity profusion 1/0 or greater as abnormal. Prevalence rose with age and with time since first exposure, from 1.6% before exposure to 26.6% more than 20 years after it. A model was built from these films and then tested on new X-rays of 74 men. Both readers agreed on 60 of those films, and among these 60 the model's predicted numbers of abnormal films fitted the observed numbers well. The estimates below excluded compensation claimants. Among 2748 men known to be alive in Australia, the model estimated prevalence at the end of 1980 at 16.4% (95% confidence interval 15.9% to 16.9%), about 450 men. Among 5241 men not known to have died or emigrated from Australia, the estimate was 16.5% (16.1% to 16.9%), about 865 men. The authors concluded that at least 16% had uncompensated abnormality likely resulting from work exposure, and saw no apparent safe dose. They noted the changes were not diagnostic of asbestosis and that the X-rays could be biased.

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 study using chest radiographs collected retrospectively from existing records, with a logistic regression model checked against new radiographs taken in a random subsample
• Who was studied: A random one-in-six sample of 1025 former male Wittenoom workers who had not applied for compensation, drawn from 6916 known former workers. Radiographs were found for 859 men, 541 of them taken after starting work. Of 100 men in the Perth area invited for a new radiograph, 74 attended.
• Exposure: Crocidolite mining and milling at Wittenoom (1943 to 1966). Each man's cumulative exposure in fibres/cc years was estimated from his work history and 1966 airborne fibre counts.
• Main results:
  • Radiographs were retrieved for 859 of the 1025 sampled men (84%).
  • The two readers showed moderate agreement (Kendall's tau 0.50). The 781 films on which both readers agreed were used to build the model.
  • Among the retrospectively collected films, prevalence of abnormality rose with years since first exposure, from 1.6% in men not yet exposed to 26.6% more than 20 years after first exposure. It also rose with age, from 0% at age 15-24 to 22.2% at 65 and over.
  • In the final model, risk of abnormality rose with time since first exposure (after the first year) in each cumulative exposure group, most steeply in the group above 55 f/cc y. For that group the relative risk was 1.387 (95% confidence interval 1.200-1.603) per unit of log days since first exposure.
  • Of the 74 men given new radiographs, both readers agreed that abnormality was present in 10 and absent in 50, and disagreed on 14.
  • The model was tested on the 60 consensus films from the recently invited men. Its expected numbers of abnormal films were compared with the observed numbers across three predicted-risk groups, and the fit was good (Hg statistic 0.90).
  • In the men given new radiographs, no other variable, including ever/never smoking, significantly improved the fit beyond the model's risk score.
  • The first prevalence estimate covered men known to be alive and living in Australia on 31 December 1980. The second covered men not known to have died or permanently emigrated from Australia by that date. Both excluded men who had claimed compensation for asbestosis before that date.
  • Estimated prevalence at 31 December 1980 among 2748 men known to be alive was 16.4% (95% confidence interval 15.9%-16.9%), or about 450 men.
  • Estimated prevalence among 5241 men not known to be dead or to have permanently left Australia was 16.5% (95% confidence interval 16.1%-16.9%), or about 865 men.
  • The authors estimated that between 450 and 900 former workers had apparently unrecognised radiographic abnormality at the end of 1980.
  • Among the ten agreed abnormal cases in the new radiographs, estimated total exposure ranged up to 120 f/cc y, and three men had less than 5 f/cc y.
• The authors' conclusion: The authors concluded that at least 16% of former Wittenoom workers had uncompensated radiographic abnormality consistent with pneumoconiosis. They considered this abnormality related to work exposure and a likely result of it, and said their data showed no apparent 'safe dose'.
• Limitations the authors state:
  • The main weakness was possible bias, especially in the retrospectively collected radiographs.
  • Post-employment radiographs could be found for only 52% of the sample.
  • Teaching hospital films may be biased toward men in ill health, and Perth Chest Clinic films toward healthy men.
  • Men living near Perth, who formed the current sample, may not represent all former workers.
  • Smoking data were only an ever/never variable, available only for the recently X-rayed men.
  • The readers often disagreed on films with low profusion scores.
  • The radiographic changes measured are not diagnostic of asbestosis.
  • Follow-up was substantially incomplete, so minimum and maximum estimates were given.
  • Earlier exposures were estimated from 1966 fibre counts, although counts for mill workers were probably higher before 1957.

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, Pneumoconiosis, Chest X-Ray, ILO Classification, Cumulative Exposure.

Related studies

• 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)
• Malignant mesotheliomas in former miners and millers of crocidolite at Wittenoom (Western Australia) after more than 50 years follow-up — G. Berry, A. Reid, et al. (2012)
• Benign and malignant pleural effusions in former Wittenoom crocidolite millers and miners — W.O. Cookson, N.H. De Klerk, et al. (1985)
• Sputum asbestos bodies and radiographic changes in residents of Wittenoom, Western Australia — A.W. Musk, J.E. Baker, et al. (1983)
• 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)
• Mortality of former crocidolite (blue asbestos) miners and millers at Wittenoom — A.W. Musk, N.H. de Klerk, et al. (2008)

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