A population-based case-control study of mesothelioma deaths among U.S. railroad workers

Our plain-English summary of A population-based case-control study of mesothelioma deaths among U.S. railroad workers, by M.B. Schenker, E. Garshick, A. Muñoz, et al (The American Review of Respiratory Disease, 1986).

The study

• Authors: M.B. Schenker, E. Garshick, A. Muñoz, S.R. Woskie, F.E. Speizer
• Journal: The American Review of Respiratory Disease
• Published: 1986;134(3):461-5
• Cited by: 24 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. 000432).

Abstract

We have completed a case-control analysis of mesothelioma deaths among current and retired U.S. railroad employees. Cause-specific death certificates were obtained for 87% of 15,059 deaths reported by the railroad retirement board, and 20 mesotheliomas were identified according to death certificate diagnosis. A 10:1 matched analysis with railroad workers dying of nonmalignant, nonaccidental causes yielded a very strong association with prior railroad work in jobs with potential asbestos exposure (odds ratio = 7.2, 95% lower confidence limit = 3.3). Consideration of railroad occupations with regular asbestos exposures (e.g., skilled trades, steam locomotive repair) yielded an odds ratio of 21.4 (95% lower confidence limit = 8.7), but the occupations with potential intermittent exposure (e.g., engineers, firemen, carmen) yielded a nonsignificant odds ratio of 2.3 (95% lower confidence limit = 0.5). Applying mesothelioma mortality rates from this study to the population of U.S. railroad workers at risk yields an estimate of 416 cases of mesothelioma occurring among U.S. railroad workers between 1981 and 2000.

In plain English

This case-control study examined deaths of male U.S. railroad workers, current and retired, who were born after January 1, 1900 and died between March 1, 1981 and February 28, 1982. Death certificates were obtained for 87% of 15,059 reported deaths, and 20 listed mesothelioma. Only 4 of these specified the lung or pleura. Each case was matched with 10 railroad workers who died of causes other than cancer, accident or suicide. Asbestos exposure was assigned by job category, and fiber types were not named. Compared with unexposed jobs, the odds ratio for mesothelioma was 7.2 (lower 95% confidence limit 3.3) for any asbestos-exposed job. It was 21.4 (lower limit 8.7) for "regular" exposure jobs, such as machinists and boilermakers. For "intermittent" jobs, such as engineers and firemen, it was 2.3 (lower limit 0.5), which was not statistically significant. The authors projected 416 cases among U.S. railroad workers from 1981 to 2000. A pathologist confirmed mesothelioma in 5 of 12 reviewed cases. The authors concluded that their findings did not reflect an "epidemic".

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: Population-based matched case-control study of death records (10 control subjects per case), with mortality rates and a projection of future cases
• Who was studied: Male current and retired U.S. railroad workers in the Railroad Retirement Board system, born after January 1, 1900, who died between March 1, 1981 and February 28, 1982. There were 15,059 reported deaths, with cause-specific death certificates for 87%. The study included 20 mesothelioma cases and 200 control subjects who died of causes other than malignancy, accident, or suicide.
• Exposure: Asbestos exposure was assigned from the earliest available railroad job category, and fiber types were not specified. "Regular" exposure covered hostlers and skilled trades in engine houses where steam locomotives were repaired (machinists, boilermakers, apprentices, laborers). "Intermittent" exposure covered engineers, firemen, carmen, carpenters, masons and construction trades. All other jobs were treated as unexposed.
• Main results:
  • Of the 20 mesothelioma cases, 4 were recorded as mesothelioma of the lung or pleura. The rest were recorded as mesothelioma not further specified.
  • 13 of the 20 cases (65%) were shop workers in the "regular" asbestos category, and 3 more were in "intermittent" categories.
  • Among control subjects, 74 of 200 (37%) were in asbestos-exposed jobs, and 30 (15%) were in the "regular" category.
  • Any asbestos-exposed job versus none: odds ratio 7.2, lower 95% confidence limit 3.3.
  • "Regular" asbestos exposure jobs versus none: odds ratio 21.4, lower 95% confidence limit 8.7.
  • "Intermittent" exposure jobs (e.g., engineers, firemen, carmen) versus none: odds ratio 2.3, lower 95% confidence limit 0.5. This was not statistically significant.
  • Time from start of work to death was 20 years or more in all cases (median 46.5 years). It was 30 years or more for the 16 cases in asbestos-exposed job categories.
  • Ever-smoking was reported for 8 of 13 cases (62%) and 133 of 164 control subjects (81%). The authors reported this difference as not significant.
  • Pathologic material was reviewed for 12 cases, and mesothelioma was confirmed in 5. In 2 more it was an alternative diagnosis; 2 were read as adenocarcinoma, 1 as possible adenocarcinoma, and 2 were nondiagnostic.
  • Applying the study's rates to the estimated population at risk gave a projection of 416 mesothelioma cases among current and retired U.S. railroad workers between 1981 and 2000.
• The authors' conclusion: The authors stated that they confirmed the association of mesothelioma with specific railroad job categories (skilled trades, steam locomotive repair). They reported that overall mesothelioma mortality rates in the railroad industry were similar to general-population rates, and that steam locomotive repair effectively ended in the 1950s. They concluded that their findings should not be considered to reflect an "epidemic" among railroad workers.
• Limitations the authors state:
  • Cases were identified from death certificates only, which the authors said probably undercounts mesotheliomas, perhaps by a factor of 2.
  • Because there were few cases, the authors could not use a measure of asbestos years worked in the risk model.
  • The projection left out workers born before 1900 and female workers, both of whom were outside the study population.
  • The projection also left out workers younger than 50 in 1981.

Topics

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

Medical terms in this study, explained in our Lexicon: Case-Control Study, Mesothelioma, Death Certificate, Asbestos Exposure, Odds Ratio.

Related studies

• A case-control study of lung cancer and diesel exhaust exposure in railroad workers — E. Garshick, M.B. Schenker, et al. (1987)
• A retrospective cohort study of lung cancer and diesel exhaust exposure in railroad workers — E. Garshick, M.B. Schenker, et al. (1988)
• Past exposure to asbestos among active railroad workers — E. Garshick, M.B. Schenker, et al. (1987)
• A case-control study relating railroad worker mortality to diesel exhaust exposure using a threshold regression model — M.L. Lee, G.A. Whitmore, et al. (2009)
• Roentgenographic evidence of asbestos exposure in a select population of railroad workers — M.J. Sepulveda, J.A. Merchant (1983)
• Insulation workers in Belfast. 1. Comparison of a random sample with a control population — W.F. Wallace, J.H. Langlands (1971)

Browse more research in The American Review of Respiratory Disease, or return to medical research.