A case-control study of lung cancer and diesel exhaust exposure in railroad workers

Our plain-English summary of A case-control study of lung cancer and diesel exhaust exposure in railroad workers, by E. Garshick, M.B. Schenker, A. Muñoz, et al (The American Review of Respiratory Disease, 1987).

The study

• Authors: E. Garshick, M.B. Schenker, A. Muñoz, M. Segal, T.J. Smith, S.R. Woskie, S.K. Hammond, F.E. Speizer
• Journal: The American Review of Respiratory Disease
• Published: 1987;135(6):1242-8
• Cited by: 119 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. 000968).

Abstract

A case-control study of deaths among U.S. railroad workers was conducted to test the hypothesis that lung cancer is associated with exposure to diesel exhaust. Employed and retired male workers with greater than or equal to 10 yr of service who were born on or after January 1, 1900 and who died between March 1, 1981 and February 28, 1982 were eligible. We collected 87% of the death certificates from 15,059 deaths reported to the U.S. Railroad Retirement Board (RRB). Cases of lung cancer (1,256) were matched to controls by age (+/- 2.5 yr) and date of death (+/- 31 days). Potential exposure to diesel exhaust was assigned based on an industrial hygiene evaluation of jobs and work areas. Each subject's work history was determined from a yearly job report filed by his employer with the RRB from 1959 until death or retirement. Asbestos exposure prior to 1959 was categorized by the job held in 1959, the end of the steam locomotive era, or by the last job held if retirement occurred before 1959. Smoking histories were obtained by questionnaire from next of kin. Using multiple conditional logistic regression analysis to adjust for smoking and asbestos exposure, workers 64 yr of age or younger at the time of death with work in a diesel exhaust exposed job for 20 yr had a significantly increased relative odds (odds ratio = 1.41, 95% Cl = 1.06, 1.88) of lung cancer. No effect of diesel exhaust exposure was seen in workers 65 yr of age or older because many of these men retired shortly after the transition to diesel-powered locomotives.(ABSTRACT TRUNCATED AT 250 WORDS)

In plain English

This case-control study tested whether lung cancer in U.S. railroad workers was linked to diesel exhaust. Subjects were male workers born from 1900 on, with 10 or more years' service, who died March 1, 1981 to February 28, 1982. Each lung cancer death was matched by age and death date to up to two deaths without cancer. Yearly job records from 1959 gave work histories; an industrial hygiene evaluation classed jobs as diesel-exposed or not. Past asbestos exposure, mainly from steam-era boiler repair, was assigned from the 1959 or earlier job, or the last job for those retiring before 1959. Smoking histories came from next of kin. In workers 64 or younger at death, 20 diesel-exposed years gave an odds ratio of 1.41 (95% CI 1.06 to 1.88), adjusted for smoking and asbestos. No diesel effect appeared at 65 or older; many retired soon after diesel locomotives arrived. Younger cases had slightly, not significantly, more asbestos exposure (25%) than controls (22%). The authors concluded the study supports the hypothesis that diesel exhaust raises lung cancer risk, pending confirmation by other studies.

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: Case-control study of deaths. Lung cancer cases were matched to controls, with smoking information collected by questionnaire from next of kin.
• Who was studied: Male U.S. railroad workers with 10 or more years of service, born in 1900 or later, who died between March 1, 1981 and February 28, 1982. Death certificates were obtained for about 87% of 15,059 reported deaths, and 1,374 lung cancer cases were identified. Analysis included 335 cases aged 64 or younger and 921 cases aged 65 or older at death, with 2,385 controls in total.
• Exposure: Diesel exhaust exposure was assigned to jobs as yes or no, based on an industrial hygiene evaluation. It was totaled as 'diesel-years' from yearly job records, from 1959 to death or retirement. Past asbestos exposure (regular, intermittent or none) came mostly from repair of asbestos-insulated steam locomotive boilers. It was assigned from the job held in 1959, or an earlier job if available, or the last job if the worker retired before 1959. No fiber type is named.
• Main results:
  • Workers aged 64 or younger at death: 20 years of diesel exhaust exposure gave an odds ratio for lung cancer of 1.41 (95% CI 1.06, 1.88), adjusted for asbestos exposure and pack-years of smoking.
  • Workers aged 64 or younger at death, compared with 0 to 4 diesel-years: 20 or more diesel-years had an odds ratio of 1.64 (95% CI 1.18, 2.29).
  • Workers aged 64 or younger at death, compared with 0 to 4 diesel-years: 5 to 19 diesel-years had an odds ratio of 1.02 (95% CI 0.72, 1.45).
  • Workers aged 65 or older at death, adjusted for smoking and asbestos: the odds ratio was 0.95 (95% CI 0.79, 1.13) for 5 to 19 years of diesel exposure and 0.94 (95% CI 0.56, 1.59) for 20 or more years.
  • Younger group, with diesel repair shop workers (those most likely to have past asbestos exposure) entered separately: 20 or more years of exposure in the other diesel jobs gave an odds ratio of 1.55 (95% CI 1.09, 2.21).
  • Younger group, excluding diesel exposure in the 5 years before death: the odds ratio was 1.43 (95% CI 1.06, 1.94) for 15 years of cumulative exposure.
  • Younger group: 25% of cases and 22% of controls had asbestos exposure, a difference that was not statistically significant.
  • Older group: slightly more controls than cases had asbestos exposure.
• The authors' conclusion: The authors concluded that the study supports the hypothesis that occupational exposure to diesel exhaust increases lung cancer risk.
• Limitations the authors state:
  • The small group of workers with past heavy asbestos exposure could not be identified individually.
  • Smoking information came from next of kin and was incomplete, so pack-years could not be calculated for everyone.
  • Diesel exposure may have been misclassified because job classification codes were used as a stand-in for exposure.
  • Each year of diesel exposure was treated as equal across all exposed job locations.
  • Final confirmation of the results awaits other studies.

Topics

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

Medical terms in this study, explained in our Lexicon: Case-Control Study, Lung Cancer, Death Certificate, Industrial Hygiene, Work History, Asbestos Exposure, Odds Ratio.

Related studies

• A retrospective cohort study of lung cancer and diesel exhaust exposure in railroad workers — E. Garshick, M.B. Schenker, et al. (1988)
• 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)
• Past exposure to asbestos among active railroad workers — E. Garshick, M.B. Schenker, et al. (1987)
• Occupational exposure to diesel motor exhaust and risk of lung cancer by histological subtype: a population-based case-control study in Swedish men — A. Ilar, N. Plato, et al. (2017)
• A population-based case-control study of mesothelioma deaths among U.S. railroad workers — M.B. Schenker, E. Garshick, et al. (1986)
• Asbestos-related disease in railroad workers. A cross-sectional study — L.C. Oliver, E.A. Eisen, et al. (1985)

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