Mortality Update of a Cohort of Canadian Petroleum Workers

Our plain-English summary of Mortality Update of a Cohort of Canadian Petroleum Workers, by A.R. Schnatter, N.C. Wojcik, G. Jorgensen (Journal of Occupational and Environmental Medicine, 2019).

The study

• Authors: A.R. Schnatter, N.C. Wojcik, G. Jorgensen
• Journal: Journal of Occupational and Environmental Medicine
• Published: 2019;61(3):225-238
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objective: This study updates the mortality experience of over 25,000 workers in a large Canadian petroleum company through December 31, 2006.

Methods: Standardized mortality ratios were generated for all-cause and specific cause mortality.

Results: All cause and all cancer mortality were favorable compared with the general Canadian population. Cancers of previous interest were largely consistent with expectation. There is a continuing excess of mesothelioma, which is of similar magnitude as the previous update, although based on larger numbers. This excess is mostly attributable to men who died in their 50s and 60s and who worked in the refining sector.

Conclusion: Most causes of death show mortality rates lower than the Canadian general population. Given the excess of mesothelioma observed, this study supports ongoing vigilance in asbestos exposure control programs, as refineries continue to remove asbestos from their facilities.

In plain English

This retrospective cohort study followed 29,379 Canadian petroleum company workers for deaths through December 31, 2006. All were hired from 1964 onward and worked at least a year; deaths were compared with Canadian general population rates. Specific exposures, including asbestos, were not measured; workers were grouped by operating segment, job group and exposure status. Overall, 1669 deaths occurred against 2418.5 expected (SMR 0.69, 95% CI 0.66 to 0.72), and lung cancer deaths were fewer than expected. The only statistically significant excess for the whole cohort was mesothelioma: 9 deaths against 2.8 expected (SMR 3.27, 95% CI 1.50 to 6.21). Adding cases from older death certificates and a cancer registry gave 15 cases against 5.4 expected (SIR 2.79, 95% CI 1.56 to 4.60). Eleven of the 15 had worked in refining, where 1.0 case was expected (SIR 10.9, 95% CI 5.45 to 19.5). All 15 were in their 50s or 60s. The authors noted possible asbestos exposure before joining the company and missing smoking data. They concluded that the persisting mesothelioma excess supports ongoing vigilance in asbestos exposure control.

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 (an update of earlier follow-up of the same cohort), comparing deaths with Canadian general population rates using standardized mortality ratios
• Who was studied: 29,379 employees (19,942 men, 9,437 women) of a large Canadian petroleum company, hired from 1964 through 2006 with at least one year of employment, followed for deaths from 1964 to December 31, 2006 (702,906 person-years); 3564 were counted as lost to follow-up
• Exposure: Work in the petroleum industry (refining, petrochemical, upstream, transportation and other segments; maintenance, operations, distribution and other job groups). Specific exposures, including asbestos, were not measured in this update, and no fiber type is named. Exposure was represented by surrogates such as operating segment, job type, duration of employment and general exposure to operations.
• Main results:
  • Whole cohort, all causes: 1669 deaths observed versus 2418.5 expected, SMR 0.69 (95% CI 0.66 to 0.72)
  • Whole cohort: lung cancer deaths were lower than expected, as were colon and kidney cancer deaths (lung: 168 observed versus 233.9 expected, SMR 0.72, 95% CI 0.61 to 0.84)
  • Whole cohort, mesothelioma deaths (10th revision coding): 9 observed versus 2.8 expected, SMR 3.27 (95% CI 1.50 to 6.21). This was the only significant excess.
  • Refinery workers, mesothelioma deaths: 6 observed versus 0.6 expected, SMR 9.93 (95% CI 3.64 to 21.60)
  • Workers ever in an exposed job, mesothelioma deaths: 6 observed versus 1.7 expected, SMR 3.53 (95% CI 1.30 to 7.69)
  • Whole cohort, mesothelioma cases including those found in earlier death certificates and the cancer registry: 15 observed versus 5.4 expected, SIR 2.79 (95% CI 1.56 to 4.60)
  • Refinery segment, mesothelioma cases: 11 of the 15 cases versus 1.0 expected, SIR 10.9 (95% CI 5.45 to 19.5)
  • All 15 mesothelioma cases were in their 50s and 60s at death or diagnosis. Ten were in maintenance or operations jobs and had worked 11 to 32 years.
  • Of the 9 mesothelioma deaths, 5 were among workers hired at ages 25 to 35 (SMR 4.89, 95% CI 1.59 to 11.41). The authors read this as indicating possible exposure before joining the company.
  • Amyotrophic lateral sclerosis (ALS), whole cohort: 15 deaths versus 8.8 expected, SMR 1.70 (95% CI 0.95 to 2.80), not statistically significant. Among nonexposed workers, 10 cases gave a significant SMR of 2.48 (95% CI 1.19 to 4.56).
• The authors' conclusion: The authors concluded that the clearest finding was a continuing excess of mesothelioma, concentrated in refinery workers and maintenance trades, who have a higher potential for asbestos exposure. They wrote that this supports ongoing vigilance in asbestos exposure control programs as refineries continue to remove asbestos.
• Limitations the authors state:
  • The cohort is still young, so risk estimates are relatively imprecise, especially for rarer causes of death
  • Comparison with the general population means a healthy worker effect is probable
  • There was no information on smoking or drinking
  • Exposure was represented only by surrogates such as job, segment and duration of employment
  • 3564 workers were potentially lost to follow-up, a larger share than usual
  • Cancer incidence data were found to be unreliable
  • Asbestos exposure in earlier jobs elsewhere could make the latency seen in this cohort appear shorter than it was

Topics

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

Medical terms in this study, explained in our Lexicon: standardized mortality ratio (SMR), Mesothelioma, Asbestos Exposure.

Related studies

• Mortality and cancer morbidity in a cohort of Canadian petroleum workers — R.J. Lewis, A.R. Schnatter, et al. (2003)
• Update of mortality and cancer incidence in the Australian petroleum industry cohort — R.T. Gun, N. Pratt, et al. (2006)
• Updated mortality among diverse operating segments of a petroleum company — R.J. Lewis, A.R. Schnatter, et al. (2000)
• Update of a prospective study of mortality and cancer incidence in the Australian petroleum industry — R.T. Gun, N.L. Pratt, et al. (2004)
• Lung cancer incidence in Canadian petroleum workers — A.R. Schnatter, M.J. Nicolich, et al. (2012)
• An updated study of mortality among workers at a petroleum manufacturing plant — Y. Honda, E. Delzell, et al. (1995)

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