Mortality among shipyard Coast Guard workers: a retrospective cohort study

Our plain-English summary of Mortality among shipyard Coast Guard workers: a retrospective cohort study, by S. Krstev, P. Stewart, J. Rusiecki, et al (Occupational and Environmental Medicine, 2007).

The study

• Authors: S. Krstev, P. Stewart, J. Rusiecki, A. Blair
• Journal: Occupational and Environmental Medicine
• Published: 2007;64(10):651-8
• Cited by: 39 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: The mortality experience of 4702 (4413 men and 289 women) civilian workers in a US Coast Guard shipyard was evaluated.

Methods: All workers employed at the shipyard between 1 January 1950 and 31 December 1964 were included in the study and were followed through 31 December 2001 for vital status. Detailed shipyard and lifetime work histories found in the shipyard personnel records and job descriptions were evaluated. Workers were classified as likely exposed to any potential hazardous substances. In addition, 20 job groups were created on likely similar exposures. Standardised mortality ratios (SMRs) were calculated based on the general population of the state and adjusted for age, calendar period, sex and race.

Results: The follow-up was successful for 93.3% of the workers. Among all men employed in the shipyard, there was an excess of mortality from all causes of death (SMR 1.08; 95% CI 1.04 to 1.12), respiratory cancers (SMR 1.29; 95% CI 1.15 to 1.43), lung cancer (SMR 1.26; 95% CI 1.12 to 1.41), mesothelioma (SMR 5.07; 95% CI 1.85 to 11.03) and emphysema (SMR 1.44; 95% CI 1.01 to 1.99) and a decrease for cardiovascular diseases (OR 0.95; 95% CI 0.90 to 1.00), vascular lesions of the central nervous system (SMR 0.80; 95% CI 0.67 to 0.96), cirrhosis of the liver (SMR 0.38; 95% CI 0.25 to 0.57) and external causes of death (SMR 0.55; 95% CI 0.44 to 0.68). A similar pattern was observed for the men classified as exposed. No increasing trend of mortality was found with duration of employment in the shipyard, with the exception of mesothelioma (SMRs of 4.23 and 6.27 for <10 years and > or =10 years, respectively). In occupations with at least three cases and with an SMR of > or =1.3, the authors observed a significantly elevated mortality for lung cancer among machinists (SMR 1.60; 95% CI 1.08 to 2.29) and shipfitters, welders and cutters (SMR 1.34; 95% CI 1.07 to 1.65) and for oral and nasopharyngeal cancers among wood workers (SMR 6.20; 95% CI 2.27 to 13.50).

Conclusion: Employment in this Coast Guard shipyard revealed a small but significant excess mortality from all causes, lung cancer and mesothelioma, most of which is probably related to asbestos exposure.

In plain English

This retrospective cohort study followed 4702 civilian workers (4413 men, 289 women) employed from 1950 to 1964 at a US Coast Guard shipyard in Baltimore, Maryland, through 2001. It compared their deaths with Maryland population rates. Workers were classed by job as exposed or not exposed to any potentially hazardous substance; the article does not name asbestos fiber types. Among men, deaths from all causes (SMR 1.08), lung cancer (SMR 1.26), mesothelioma (6 deaths against 1.2 expected; SMR 5.07, 95% CI 1.85 to 11.03) and emphysema (SMR 1.44) were significantly higher than expected. All six mesothelioma deaths were in men classed as exposed. Lung cancer was raised in both exposed and non-exposed men, but was statistically significant only in the exposed group. Machinists, and shipfitters, welders and cutters, had significantly raised lung cancer death rates. No women died of mesothelioma. The authors concluded that the excesses were probably related, at least in part, to asbestos exposure. They lacked smoking information but judged tobacco unlikely to explain the findings.

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 cohort mortality study comparing deaths with the general population of Maryland using standardised mortality ratios (SMRs), adjusted for age, calendar period, sex and race
• Who was studied: 4702 civilian workers (4413 men and 289 women) employed at the US Coast Guard shipyard in Baltimore, Maryland, between 1 January 1950 and 31 December 1964, followed for vital status through 31 December 2001. 4389 (93.3%) were traced, and there were 3331 deaths. Women were left out of most analyses because there were few of them.
• Exposure: Shipyard employment. Workers who ever held typical shipbuilding and repair jobs were classed as exposed to any potentially hazardous substance; those who never did (mainly managers and office workers) were classed as non-exposed. Workers were also grouped into 20 job groups, and duration of employment was split at less than 10 years versus 10 years or more. Asbestos is discussed as a likely exposure, but no fiber types or measured doses are reported.
• Main results:
  • All men: deaths from all causes were higher than expected, with 3210 observed against 2974.8 expected (SMR 1.08; 95% CI 1.04 to 1.12)
  • All men: there were 6 mesothelioma deaths against 1.2 expected (SMR 5.07; 95% CI 1.85 to 11.03)
  • All men: there were 305 lung cancer deaths against 242.0 expected (SMR 1.26; 95% CI 1.12 to 1.41)
  • All men: there were 36 emphysema deaths against 25.1 expected (SMR 1.44; 95% CI 1.01 to 1.99)
  • Men classed as exposed had a mesothelioma SMR of 5.39 (95% CI 1.97 to 11.74, 6 deaths). No mesothelioma deaths occurred among non-exposed men.
  • Lung cancer SMR was 1.26 (95% CI 1.11 to 1.41; 286 deaths) in exposed men and 1.33 (95% CI 0.80 to 2.07; 19 deaths) in non-exposed men. The non-exposed result was not statistically significant.
  • Mesothelioma by duration of employment among men: SMR 4.25 (95% CI 0.85 to 12.42; 3 deaths) for less than 10 years, and SMR 6.27 (95% CI 1.26 to 18.32; 3 deaths) for 10 years or more
  • Lung cancer mortality was significantly raised among machinists (SMR 1.60; 95% CI 1.08 to 2.29) and among shipfitters, welders and cutters (SMR 1.34; 95% CI 1.07 to 1.65)
  • Oral and nasopharyngeal cancer mortality was raised among wood workers (6 deaths; SMR 6.20; 95% CI 2.27 to 13.50)
  • Mesothelioma mortality was increased in every job group that had a mesothelioma death, but no group had more than two deaths
  • Among women, no SMRs were significantly raised or lowered, and there were no mesothelioma deaths
  • Only one asbestosis death was observed in the cohort
• The authors' conclusion: The authors concluded that employment in this shipyard was associated with a small but significant excess of deaths from all causes, lung cancer, mesothelioma and emphysema. They judged this probably related, at least in part, to asbestos exposure.
• Limitations the authors state:
  • The study had no information on tobacco use. The authors judged it unlikely that smoking explained the findings, because most tobacco-related diseases were not elevated.
  • The share of workers who could not be traced was somewhat larger than preferred
  • Asbestosis is often not listed as a cause of death on death certificates, which probably explains why only one asbestosis death was found
  • The mesothelioma comparison by duration of employment was based on small numbers
  • Women were too few for most analyses
  • The data could not separate work-related accidental deaths from non-work accidents

Topics

The National Library of Medicine indexes this study under subjects our site covers: Shipyards and maritime work.

Medical terms in this study, explained in our Lexicon: Cohort Study, Lung Cancer, Mesothelioma, Emphysema, Asbestos Exposure.

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