Predictions of future cases of asbestos-related disease among former miners and millers of crocidolite in Western Australia

Our plain-English summary of Predictions of future cases of asbestos-related disease among former miners and millers of crocidolite in Western Australia, by N.H. de Klerk, B.K. Armstrong, A.W. Musk, et al (The Medical Journal of Australia, 1989).

The study

• Authors: N.H. de Klerk, B.K. Armstrong, A.W. Musk, M.S. Hobbs
• Journal: The Medical Journal of Australia
• Published: 1989;151(11-12):616-20
• Cited by: 41 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. 002553).

Abstract

In a cohort of 6502 male and 410 female former workers from the crocidolite (blue asbestos) mining and milling works at Wittenoom, Western Australia, there were 94 cases of malignant mesothelioma (12 cases of peritoneal mesothelioma), 141 cases of lung cancer and 356 successful compensation claims for asbestosis to the end of 1986. After adjusting for measured covariate effects by means of proportional hazards regression analysis, smooth curves were fitted to the resulting "underlying" incidence rates for malignant mesothelioma, lung cancer and asbestosis, separately, and for mortality of any cause. By the use of these curves and individual risk estimates, predictions have been made of the future incidence of these diseases to the year 2020. With the assumption that all subjects who were not known to be dead or departed overseas still were alive at December 31, 1986, and excluding persons of more than 85 years of age, the number of new cases of mesothelioma is expected to rise to a peak of around 25 cases per year in 2010, with an expected total number of 692 cases of mesothelioma (95% confidence interval [CI], 394-990 cases) between 1987 and 2020. A total of 2898 deaths (95% CI, 2284-3511 deaths) of any cause is expected in the same period. New cases of lung cancer and asbestosis are expected to continue at roughly the current rates of eight and 17 cases per year, respectively, before declining after the year 2000, leading to totals of 183 cases (95% CI, 34-335 cases) and 482 cases (95% CI, 236-728 cases), respectively, being expected by the year 2020. Predictions that were based on the censoring of subjects at the date that they last were known to be alive resulted in slightly higher, but probably less accurate, estimates.

In plain English

The authors used records of 6502 men and 410 women who had worked at the crocidolite (blue asbestos) mining and milling operation at Wittenoom, Western Australia, between 1943 and 1966. They followed this group to the end of 1986 and used it to predict asbestos-related disease up to 2020. By the end of 1986 there had been 94 cases of malignant mesothelioma (12 of them peritoneal), 141 cases of lung cancer and 356 successful compensation claims for asbestosis. The authors built statistical models of disease rates and projected them forward. They predicted that new mesothelioma cases would peak at about 25 per year around 2010, with 692 cases expected from 1987 to 2020 (95% confidence interval 394 to 990). For the same period they expected 183 lung cancer cases (95% confidence interval 34 to 335), 482 successful asbestosis claims (95% confidence interval 236 to 728) and 2898 deaths from any cause (95% confidence interval 2284 to 3511). The authors called the predictions approximate and said their confidence intervals were minimal estimates. They concluded that, without effective intervention, the mesothelioma epidemic would continue into the first decade of the next century.

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: Prediction (projection) study based on a historical cohort: Cox regression models of disease incidence, with smooth curves fitted to the underlying rates and extrapolated to 2020
• Who was studied: 6502 male and 410 female former employees of Australian Blue Asbestos at the Wittenoom crocidolite mine and mill, Western Australia, employed between 1943 and 1966 and followed up to December 31, 1986
• Exposure: Crocidolite (blue asbestos) from mining and milling. Exposure was estimated from airborne fibre measurements made in 1966 for 87 job categories, combined with a ranking of how dusty each job was in earlier periods.
• Main results:
  • To the end of 1986 the cohort had 94 cases of malignant mesothelioma of the pleura and peritoneum (12 peritoneal), 141 cases of lung cancer and 356 successful asbestosis claims
  • Predicted new mesothelioma cases in the cohort would rise to a peak of about 25 per year around 2010 and then decline
  • Expected 692 cases of mesothelioma in the cohort from 1987 to 2020 (95% CI, 394 to 990 cases)
  • Expected 183 cases of lung cancer (95% CI, 34 to 335) and 482 successful asbestosis claims (95% CI, 236 to 728) from 1987 to 2020
  • New lung cancer and asbestosis cases were expected to continue at roughly the current rates of 8 and 17 per year, then decline after 2000
  • Expected 2898 deaths from any cause in the cohort from 1987 to 2020 (95% CI, 2284 to 3511)
  • Mesothelioma incidence increased between the third and fourth power of the time since first exposure
  • An alternative method, which stopped counting each person at the date they were last known to be alive, gave 813 expected mesothelioma cases (95% CI, 491 to 1136), 201 lung cancers (45 to 361), 492 asbestosis claims (245 to 740) and 1901 deaths (1707 to 3039). The authors judged these estimates probably less accurate.
• The authors' conclusion: The authors concluded that, without some effective intervention, the mesothelioma epidemic caused by crocidolite exposure at Wittenoom would continue into the first decade of the next century. They expected asbestosis claims probably to continue at about the same level as lung cancer cases, and described the predictions as approximate but the most likely outcome given existing evidence.
• Limitations the authors state:
  • The confidence intervals ignore errors in relative risk estimation and curve fitting, so they are minimal estimates and the true error is larger
  • Errors from using an incorrect model grow as time since first exposure increases and are likely much larger than the random error shown
  • After 1980, lung cancer cases were identified from death certificates only, so non-fatal lung cancers were excluded
  • Asbestosis was counted only as successful compensation claims, which depend on many factors apart from crocidolite exposure
  • Follow-up was incomplete (vital status known for 66% of men and 52% of women), and loss to follow-up was associated with intensity and duration of exposure
  • In a single cohort, uncertainties in prediction are relatively greater the smaller the population, giving larger probable errors

Topics

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

Medical terms in this study, explained in our Lexicon: Crocidolite, Wittenoom, Mesothelioma, Peritoneal Mesothelioma, Lung Cancer, Incidence, confidence interval.

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)
• Prevalence of radiographic asbestosis in crocidolite miners and millers at Wittenoom, Western Australia — W.O. Cookson, N.H. De Klerk, et al. (1986)
• Mortality of former crocidolite (blue asbestos) miners and millers at Wittenoom — A.W. Musk, N.H. de Klerk, et al. (2008)
• Benign and malignant pleural effusions in former Wittenoom crocidolite millers and miners — W.O. Cookson, N.H. De Klerk, et al. (1985)
• Plasma vitamin concentrations and incidence of mesothelioma and lung cancer in individuals exposed to crocidolite at Wittenoom, Western Australia — H.S. Alfonso, L. Fritschi, et al. (2006)

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