A Radiological Follow-Up Study Of The Effect Of Asbestos In Dockyard Workers At Devonport

Our plain-English summary of A Radiological Follow-Up Study Of The Effect Of Asbestos In Dockyard Workers At Devonport, by G.H.G. Mcmillan, G. Sheers, R. Pethybridge (1978).

The study

• Authors: G.H.G. Mcmillan, G. Sheers, R. Pethybridge
• Published: Journal Of The Royal Naval Medical Service 64(2):88-104, Summer (1978)
• Type of article: Journal article
• Our copy: from Johns-Manville's own medical library, J-M no. 003970. The article is still under copyright, so we describe it here rather than post it.

In plain English

This study re-examined, after eleven years, a 10 per cent random sample of civilian industrial workers at HM Dockyard, Devonport, first X-rayed in 1966. Of the 1414 men examined in 1966, 168 had died by 1977, and 1012 were re-examined with chest X-rays and a questionnaire. Men were placed in four exposure groups according to their highest-risk job. Among 971 re-examined men who had no asbestos-related lesion in 1966, 97 had developed one, including six with pulmonary fibrosis and one with pleural mesothelioma. Rates were highest in group 1 and lowest in group 4. At least six of the 59 men whose changes were confined to the pleura in 1966 had developed asbestosis. In 1977, the prevalence of lesions in smokers and ex-smokers was almost three times that in non-smokers. The authors concluded that the attack rate for all asbestos lesions was approximately 10 per cent in eleven years. They cautioned that the mesothelioma estimate rested on only two cases and that differences in who responded may have affected the rates.

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: Radiological follow-up (repeat survey) of a 10 per cent random sample of dockyard workers first surveyed in 1966, re-examined after eleven years to measure attack and progression rates of asbestos-related lesions
• Who was studied: 1414 men who responded to the 1966 survey, drawn as a 10 per cent random sample of 13,040 civilian men at HM Dockyard, Devonport. By 1977, 168 (11.9%) had died. 1012 men were re-examined in 1977, which was 71.6 per cent of the 1966 responders and 81.2 per cent of survivors.
• Exposure: Occupational exposure to asbestos dust in the dockyard, with no fiber type specified. Men were assigned to four exposure groups by the occupation with the highest risk (group 1 included laggers and asbestos sprayers; group 4 was all other occupations). The authors used 1970 as the end point of all exposure.
• Main results:
  • Of 971 men with no asbestos-related lesion in 1966 who were re-examined in 1977, 97 had developed such an abnormality.
  • Among these 971 survivors, six had developed pulmonary fibrosis and one a pleural mesothelioma. This gave 11-year attack rates of approximately 10 per cent for all lesions, 0.6 per cent for pulmonary fibrosis and 0.1 per cent for mesothelioma.
  • When survivors and the dead were counted together (1129 men), the attack rate was 0.6 per cent for pulmonary fibrosis and 0.17 per cent for mesothelioma.
  • New lesions showed a dose-response pattern: rates were highest in exposure group 1 and lowest in group 4.
  • Among men with lesions in 1966 who were re-examined, four of 34 with simple plaques and one of two with diffuse pleural thickening had developed pulmonary fibrosis.
  • Including men known to have died, at least six of the 59 men whose abnormality was confined to the pleura in 1966 had developed asbestosis within 11 years.
  • Among the 152 men who had no asbestos-related lesion in 1966 and had died by 1977, one died of asbestosis, one of mesothelioma and 18 of bronchial carcinoma.
  • Four men who had an asbestos-related lesion in 1966 later died of diseases directly related to asbestos exposure. Only one of the four had not had pulmonary fibrosis in 1966.
  • Among the 1012 men examined in 1977, the overall prevalence of asbestos-related abnormalities in smokers and ex-smokers was almost three times that of non-smokers.
  • No cases of asbestos-related disease, as distinct from pleural abnormalities, were found among the non-smokers.
  • In the whole sample of 1414 men, in each age group over 25 years, the 1977 minimum prevalence exceeded the 1966 prevalence by approximately 9 per cent. The authors took this to suggest a linear relationship with the passage of time.
• The authors' conclusion: The authors concluded that the overall attack rate for all asbestos lesions was approximately 10 per cent in eleven years (about 1 per cent per year if the relationship with time is linear). They also concluded that approximately 10 per cent of men with pleural plaques or diffuse pleural thickening can be expected to develop pulmonary fibrosis within eleven years, and that smoking exerts a considerable influence on the development of these lesions.
• Limitations the authors state:
  • Response was relatively high in the higher exposure groups and relatively low in younger men, which may have inflated the observed attack rates.
  • The relatively low response in men over 64 may have had the opposite effect, lowering the observed rates.
  • Radiographic surveys are generally accepted to underestimate the true prevalence of pleural plaques.
  • The rates apply to men employed in 1966. Because of changes in exposure and high staff turnover, they cannot be applied to the 1977 workforce, where the authors expected the attack rate to be lower.
  • The mesothelioma rate (approximately 0.2 per cent) was based on only two cases and should be treated with caution.
  • The 1966 radiographs were not re-read. Instead, the 1966 diagnostic criteria were applied to the 1977 films, which excluded minor costophrenic angle blunting and all but the most obvious diaphragmatic plaques from the results.

Topics

Medical terms in this study, explained in our Lexicon: Chest X-Ray, Pulmonary Fibrosis, Pleural Mesothelioma, Pleura, Mesothelioma.

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