A cohort study of mortality among Ontario pipe trades workers

Our plain-English summary of A cohort study of mortality among Ontario pipe trades workers, by M.M. Finkelstein, D.K. Verma (Occupational and Environmental Medicine, 2004).

The study

• Authors: M.M. Finkelstein, D.K. Verma
• Journal: Occupational and Environmental Medicine
• Published: 2004;61(9):736-42
• Cited by: 16 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Aims: To study mortality in a cohort of members of the United Association of Journeymen and Apprentices of the Plumbing and Pipe Fitting Industry of the United States and Canada and to compare results with two previous proportional mortality studies.

Methods: A cohort of 25,285 workers who entered the trade after 1949 was assembled from records of the international head office. Mortality was ascertained by linkage to the Canadian Mortality Registry at Statistics Canada. Standardised mortality ratios were computed using Ontario general population mortality rates as the reference.

Results: There were significant increases in lung cancer mortality rates (SMR 1.27; 95% CI 1.13 to 1.42). Increased lung cancer risk was observed among plumbers, pipefitters, and sprinkler fitters. Increased risk was observed among workers joining the Union as late as the 1970s. A random effects meta-analysis of this study and the two PMR studies found significant increases in oesophageal (RR 1.24; 95% CI 1.00 to 1.53), lung (RR 1.31; 95% CI 1.19 to 1.44), and haematological/lymphatic (RR 1.21; 95% CI 1.08 to 1.35) malignancies.

Conclusions: The mortality pattern is consistent with the effects of occupational exposure to asbestos. Increased risk due to other respiratory carcinogens such as welding fume cannot be excluded. There are substantial amounts of asbestos in place in industrial and commercial environments. The education and training of workers to protect themselves against inhalation hazards will be necessary well into the future.

In plain English

This retrospective cohort study followed 25,285 male Ontario members of the plumbers' and pipefitters' union (the United Association) who joined the trade after 1949. Follow-up ran to the end of 1999. Deaths were identified through the Canadian Mortality Registry and compared with death rates for Ontario men. In the first 20 years after joining, deaths were generally below the population average. Twenty or more years after joining, there were 317 lung cancer deaths across all trades, a standardised mortality ratio of 1.27 (95% CI 1.13 to 1.42). Plumbers and sprinkler fitters who joined in the 1970s also showed increased lung cancer risk. Deaths from mesothelioma and asbestosis were recorded. When this study was pooled with two earlier American studies of the union, there were significant increases in oesophageal, lung, and blood and lymphatic cancers. The authors concluded that the occurrence of mesothelioma and asbestosis confirmed that occupational asbestos exposure played a role. They said they could not separate the effects of other lung carcinogens such as welding fume, and they had no information on individual workers' tasks or exposures.

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 using standardised mortality ratios against Ontario male population rates, plus a random effects meta-analysis combining it with two earlier American proportional mortality (PMR) studies of the same union
• Who was studied: 25,285 male Ontario members of the United Association of Journeymen and Apprentices of the Plumbing and Pipe Fitting Industry who entered the trade after 1949. Follow-up was to the end of 1999. Trade groups were pipefitters (4211), refrigeration fitters (3149), plumbers (10877) and sprinkler fitters (7048).
• Exposure: Work in the pipe trades. Possible exposures named by the authors include asbestos, metal fumes and gases from welding, brazing and soldering, and solvents used to join plastic pipe. Asbestos fiber types were not specified, and no individual exposure data were available.
• Main results:
  • Earlier than 20 years after joining the union, observed mortality among members was generally below the population average, which the authors described as the healthy worker effect.
  • Twenty or more years after joining, all trades combined had 317 lung cancer deaths, SMR 1.27 (95% CI 1.13 to 1.42).
  • Lung cancer twenty or more years after joining, by trade:
• pipefitters: 98 deaths, SMR 1.36 (95% CI 1.1 to 1.7)
• refrigeration fitters: 10 deaths, SMR 0.68 (0.32 to 1.2)
• plumbers: 119 deaths, SMR 1.19 (0.99 to 1.4)
• sprinkler fitters: 90 deaths, SMR 1.43 (1.2 to 1.8)
  • Lung cancer 20 to 29 years after joining, by trade:
• pipefitters: SMR 1.18 (95% CI 0.85 to 1.60)
• plumbers: SMR 1.32 (95% CI 1.01 to 1.69)
• sprinkler fitters: SMR 1.53 (95% CI 1.12 to 2.05)
  • Among plumbers and sprinkler fitters who joined during the 1970s, increased lung cancer risk was apparent. Among pipefitters who joined after 1969 there was as yet no indication of increased risk; the authors noted small numbers and that the high-risk period after 30 years had not yet been reached.
  • One death from mesothelioma and one from asbestosis occurred earlier than 20 years after joining. Three mesothelioma deaths occurred 20 to 29 years after joining.
  • Twenty or more years after joining, increases in oesophageal and colorectal cancer deaths were not statistically significant. Oesophageal cancer: 30 deaths, SMR 1.27 (95% CI 0.86 to 1.81), all trades.
  • Deaths from circulatory disease (heart disease and stroke) among members were below expectation. For deaths 10 or more years after joining, the SMR was 0.87 (95% CI 0.83 to 0.93), all trades.
  • Combining this Ontario study with the two American PMR studies gave a lung cancer relative risk of 1.31 (95% CI 1.19 to 1.44).
  • The combined relative risk for oesophageal cancer across the three studies was 1.24 (95% CI 1.00 to 1.53), which the authors reported as statistically significant.
  • The combined relative risk for blood and lymphatic cancers across the three studies was 1.21 (95% CI 1.08 to 1.35). In the Ontario cohort alone, the blood and lymphatic SMR was 1.14 (95% CI 0.89 to 1.44).
  • The authors estimated how much higher smoking alone might make lung cancer risk among plumbers and pipefitters. Using 1987 to 1990 US smoking rates, they got a relative risk of about 1.24. They said the observed lung cancer risk was modestly higher than this, but both estimates were uncertain.
• The authors' conclusion: The authors concluded that the mortality pattern was consistent with occupational asbestos exposure. They stated that the occurrence of mesothelioma and asbestosis confirms that occupational asbestos exposure played a role in these workers' health.
• Limitations the authors state:
  • Deaths were found by probabilistic record linkage, so some deaths may have been missed and some living people wrongly classified as dead.
  • Many causes of death and time intervals were tested, so some significant findings may be due to chance.
  • There was no information on individual work activities or personal exposures, so the risks are an average over the workforce.
  • 2466 members expelled for non-payment of dues had to be excluded; their risks may have differed.
  • Trade codes came from the union and may have been misclassified, which could blunt differences between trades.
  • The effects of other lung carcinogens, such as welding fume, could not be separated from those of asbestos.

Topics

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

Medical terms in this study, explained in our Lexicon: Cohort Study, Proportional mortality, Lung Cancer, Pipefitter, Meta-Analysis, Occupational Exposure.

Related studies

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• Mortality among employees of an Ontario factory manufacturing insulation materials from amosite asbestos — M.M. Finkelstein (1989)
• Radiographic asbestosis is not a prerequisite for asbestos-associated lung cancer in Ontario asbestos-cement workers — M.M. Finkelstein (1997)
• Mortality among employees of an Ontario asbestos-cement factory — M.M. Finkelstein (1984)
• Mortality among long-term employees of an Ontario asbestos-cement factory — M.M. Finkelstein (1983)
• An updated historical cohort mortality study of workers exposed to asbestos in a refitting shipyard, 1947-2007 — K. Tomioka, Y. Natori, et al. (2011)

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