The rise and fall in incidence of malignant mesothelioma from a British Naval Dockyard, 1979-1999

Our plain-English summary of The rise and fall in incidence of malignant mesothelioma from a British Naval Dockyard, 1979-1999, by A.K. Hilliard, J.K. Lovett, C.R. McGavin (Occupational Medicine, 2003).

The study

• Authors: A.K. Hilliard, J.K. Lovett, C.R. McGavin
• Journal: Occupational Medicine
• Published: 2003;53(3):209-12
• Cited by: 33 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: The incidence of malignant mesothelioma in Britain is predicted to rise over the next 15-25 years because of past failure to protect the workforce against inhalation of asbestos. In British Naval dockyards, alternative insulation materials and respiratory protection were introduced from the mid-1960s. Aims This study was carried out to investigate the effects of these control measures on mesothelioma deaths in dockyard workers.

Methods: Cases of mesothelioma of the pleura and peritoneum between 1979 and 1999 in workers from the Devonport Naval Dockyard, south-west England, were sought from coroners' and medico-legal records.

Results: Three hundred and one cases were identified, 7% peritoneal. The peak incidence occurred in 1991 with 25 cases per annum (quadratic model fit R(2) = 74.2%, P < 0.001) and we predict that by 2003 the incidence will fall to fewer than five cases per annum. The mean time between first exposure and presentation was 48.5 years [95% confidence interval (CI) = 47.3-49.8], but this was significantly shorter in the more heavily exposed trades, when compared with the less heavily exposed (42 years, 95% CI = 39.0-45.0, versus 49.5 years, 95% CI = 48.2-50.9). Those with higher exposure were also at significantly greater risk of peritoneal disease (P < 0.023, Fisher's exact test).

Conclusion: The reduction in incidence of mesothelioma is greater than can be accounted for by reduction in numbers of dockyard workers over the last 50 years. Changes in insulation materials and improved industrial hygiene measures introduced into the Devonport Dockyard from the mid-1960s have resulted in an earlier decline in the incidence of malignant mesothelioma than that predicted for the British workforce as a whole.

In plain English

The authors searched coroners' and medico-legal records for 1979–1999 deaths from pleural and peritoneal malignant mesothelioma among people who had worked at least 6 months at the Devonport Naval Dockyard, south-west England. The yard had used crocidolite, amosite and chrysotile, adding alternative insulation and respiratory protection from the 1960s. The authors found 301 deaths, peaking in 1989–1994. A statistical model suggested the death rate fell 35% between 1991 and 1999 and forecast fewer than five deaths a year by 2003. The average time from first exposure to disease presentation was 48.5 years (95% confidence interval 47.3 to 49.8). It was significantly shorter in 41 workers from 'continuously exposed' trades (42.0 years, 95% CI 39.0 to 45.0) than in 241 from 'intermittently exposed' trades (49.5 years, 95% CI 48.2 to 50.9). Twenty-one cases (7%) were peritoneal, with a statistically significant excess among continuously exposed workers (7 of 41 with data). The authors concluded the decline was greater than a smaller workforce would explain and attributed it to the dockyard's control measures. They noted some cases may have been missed.

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: Descriptive case series of mesothelioma deaths found through coroners' and medico-legal records, with regression (trend) analysis
• Who was studied: 301 people (two of them female) who had worked at least 6 months in the Devonport Naval Dockyard, Plymouth, south-west England, and died of pathologically confirmed malignant mesothelioma, 1979–1999. Three mesothelioma deaths in wives of workers were excluded.
• Exposure: Asbestos exposure in dockyard work. The article describes past use of crocidolite, amosite and chrysotile at the yard. Trades were grouped as 'continuously' exposed (laggers, sprayers, painters) or 'intermittently' exposed (shipwrights, boilermakers, fitters, welders). Mean years of asbestos exposure was 22.6 (range 1–57).
• Main results:
  • 301 mesothelioma deaths were identified among dockyard workers in 1979–1999.
  • Deaths peaked in the years 1989–1994.
  • A quadratic model fitted the 1979–1999 death data (R2 = 74.2%, P < 0.001) and suggested the death rate fell by 35% between 1991 and 1999.
  • Trend analysis forecast annual deaths falling to fewer than five by 2003.
  • For all cases, the mean latent period from first exposure to disease presentation was 48.5 years (95% CI 47.3–49.8).
  • The latent period was significantly shorter in 41 workers from continuously exposed trades (42.0 years, 95% CI 39.0–45.0) than in 241 workers from intermittently exposed trades (49.5 years, 95% CI 48.2–50.9), P less than 0.001.
  • 21 cases (7%) were peritoneal mesothelioma, with a significant excess in the continuously exposed group (7 out of 41 for whom data were available; P < 0.023 as printed, Fisher's exact test).
  • The mean latent period was about the same for peritoneal and pleural disease (48.5 versus 48.6 years).
  • Mean age at death was 68.2 years (range 44–95).
• The authors' conclusion: The authors concluded that the fall in mesothelioma incidence was greater than reductions in workforce numbers can explain. They attributed the decline to changes in insulation materials and improved hygiene and respiratory protection introduced at the dockyard from the mid-1960s, which they said produced an earlier decline than predicted for the British workforce as a whole.
• Limitations the authors state:
  • Case finding may have been incomplete because of failure to diagnose or report cases to the coroner, especially in the early years and for peritoneal disease.
  • Some cases may have been missed because workers moved away from the area. Earlier work suggested fewer than 1 in 13 cases may have been missed this way.
  • The authors could not obtain accurate workforce figures for the dockyard since the Second World War.
  • Cases were found through deaths, so living cases were not detected. For this reason, 1998 and 1999 were omitted from the analysis by year of presentation.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma, Peritoneal mesothelioma, The Navy.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Respirator, Pleura, Peritoneum, confidence interval, Industrial Hygiene.

Related studies

• Correlation between fibre content of the lungs and disease in naval dockyard workers — J.C. Wagner, C.B. Moncrieff, et al. (1986)
• UK Naval Dockyards asbestosis study: survey of the sample population aged 50-59 years — C.E. Rossiter, P.G. Harries (1979)
• The health of welders in naval dockyards. The risk of asbestos-related diseases occurring in welders — G.H. McMillan (1983)
• Royal Naval dockyards asbestosis research project: nine-year follow-up study of men exposed to asbestos in Devonport Dockyard — C.E. Rossiter, J.R. Heath, et al. (1980)
• Asbestos dust concentrations in ship repairing: a practical approach to improving asbestos hygiene in naval dockyards — P.G. Harries (1971)
• UK Naval Dockyards Asbestosis Study: radiological methods in the surveillance of workers exposed to asbestos — G. Sheers, C.E. Rossiter, et al. (1978)

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