An updated historical cohort mortality study of workers exposed to asbestos in a refitting shipyard, 1947-2007

Our plain-English summary of An updated historical cohort mortality study of workers exposed to asbestos in a refitting shipyard, 1947-2007, by K. Tomioka, Y. Natori, S. Kumagai, et al (International Archives of Occupational and Environmental Health, 2011).

The study

• Authors: K. Tomioka, Y. Natori, S. Kumagai, N. Kurumatani
• Journal: International Archives of Occupational and Environmental Health
• Published: 2011;84(8):959-67
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Purpose: To evaluate the long-term health effects of occupational asbestos exposure, an updated historical cohort mortality study of workers at a refitting shipyard was undertaken.

Methods: The cohort consisted of 249 male ship repair workers (90 laggers, 159 boiler repairers). To determine relative excess mortality, standardized mortality ratios (SMRs) were calculated using mortality rates among the Japanese male population. Mortality follow-up of study subjects was performed for the period from 1947 till the end of 2007.

Results: We identified the vital status of 87 (96.7%) laggers and 150 (94.3%) boiler repairers. Of these, 63 (72.4%) and 95 (63.3%), respectively, died. Laggers, who had handled asbestos materials directly, showed a significantly elevated SMR of 2.64 (95% confidence interval [CI]: 1.06-5.44) for lung cancer and 2.49 (95% CI: 1.36-4.18) for nonmalignant respiratory diseases. Boiler repairers, who had many opportunities for secondary exposure to asbestos and a few for direct exposure, showed no significant elevation in SMR for lung cancer but a significantly elevated SMR of 1.78 (95% CI: 1.06-2.81) for nonmalignant respiratory diseases. In an analysis according to duration of employment, there was a significantly elevated SMR of nonmalignant respiratory diseases in the longer working years group. Among workers from both jobs, no deaths caused by mesothelioma in addition to those in the original study were found and no subject died from larynx cancer.

Conclusion: This updated study confirmed a significant excess of asbestos-related mortality from diseases such as lung cancer and nonmalignant respiratory diseases among workers in a refitting shipyard in Japan.

In plain English

This study updated an earlier follow-up of 249 Japanese men who worked at least six months between 1947 and 1979 at a U.S. Navy ship repair yard in Japan. There were 90 laggers (pipe coverers), who handled asbestos directly, and 159 boiler repairers, who were exposed indirectly while working near the laggers. The asbestos was considered to be chrysotile and amosite, not crocidolite. No asbestos fiber concentration data were available for this shipyard. Deaths through 2007 were compared with those expected from Japanese male death rates. Among laggers, lung cancer deaths (7) were significantly elevated, at 2.64 times expected (95% CI 1.06–5.44). Deaths from nonmalignant respiratory diseases (14, including five from asbestosis) were also elevated, at 2.49 (1.36–4.18). Among boiler repairers, lung cancer was not significantly elevated (1.61, 0.70–3.17), but nonmalignant respiratory diseases were (1.78, 1.06–2.81). No new mesothelioma deaths were found beyond the single one in the original study, and no one died of larynx cancer. The authors concluded that the update confirmed a significant excess of asbestos-related deaths. They noted that the small cohort may have limited statistical power.

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: Updated historical (retrospective) cohort mortality study using standardized mortality ratios (SMRs) against Japanese male death rates
• Who was studied: 249 Japanese men (90 laggers, 159 boiler repairers) who worked at least 6 months between 1947 and the end of 1979 at a U.S. Navy shipyard in Japan, followed to 31 December 2007. Vital status was identified for 87 laggers (63 dead) and 150 boiler repairers (95 dead).
• Exposure: Asbestos in ship repair work. Laggers had direct exposure (refitting pipes, making asbestos mattresses). Boiler repairers were exposed indirectly but continuously while working near the laggers. The asbestos was considered to be chrysotile and amosite but not crocidolite. Duration of employment was used as the measure of exposure, with a cutoff of 12 years.
• Main results:
  • Laggers: 7 lung cancer deaths, SMR 2.64 (95% CI 1.06–5.44), statistically significant
  • Laggers: deaths from nonmalignant respiratory diseases, including five from asbestosis, SMR 2.49 (95% CI 1.36–4.18)
  • Laggers employed 12 years or more: nonmalignant respiratory disease SMR 3.91 (95% CI 1.87–7.18)
  • Boiler repairers: 8 lung cancer deaths, SMR 1.61 (95% CI 0.70–3.17), not statistically significant
  • Boiler repairers: nonmalignant respiratory diseases SMR 1.78 (95% CI 1.06–2.81), statistically elevated
  • Laggers: with an assumed latent period of 10 years, the lung cancer SMR was 2.72 (95% CI 1.09–5.61)
  • No new mesothelioma deaths were found in the update. Only one case had been reported in the original study, a boiler repairer. No lagger died of mesothelioma or larynx cancer, and no boiler repairer died of larynx cancer.
  • Of the 15 lung cancer deaths across both groups, smoking history was known for 14, and only one of these was a nonsmoker
  • Histology was available for 10 of the 15 lung cancer cases: five adenocarcinomas, four squamous cell carcinomas, one large cell carcinoma
• The authors' conclusion: The authors concluded that the update confirmed a significant excess of asbestos-related mortality, such as lung cancer and nonmalignant respiratory diseases, among these refitting shipyard workers. They judged that the lung cancer deaths were likely related more to shipyard asbestos exposure than to smoking.
• Limitations the authors state:
  • The cohort was not large, which may have given inadequate statistical power
  • The actual asbestos fiber concentrations the workers were exposed to were unknown, because no fiber concentration data were available for this shipyard
  • Because most lung cancer cases were smokers, the role of smoking as a confounder or interacting factor could not be determined

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Insulator, standardized mortality ratio (SMR), confidence interval, Lung Cancer, Take-home Exposure, Mesothelioma, Laryngeal Cancer.

Related studies

• A historical cohort mortality study of workers exposed to asbestos in a refitting shipyard — N. Kurumatani, Y. Natori, et al. (1999)
• A historical cohort mortality study among shipyard workers in Genoa, Italy — R. Puntoni, F. Merlo, et al. (2001)
• An updated mortality study of workers at a petroleum refinery in Beaumont, Texas — G.K. Raabe, K.W. Collingwood, et al. (1998)
• Mortality among shipyard Coast Guard workers: a retrospective cohort study — S. Krstev, P. Stewart, et al. (2007)
• Mortality and cancer morbidity in a cohort of Canadian petroleum workers — R.J. Lewis, A.R. Schnatter, et al. (2003)
• Cohort mortality study of rock salt workers in Italy — M. Tarchi, D. Orsi, et al. (1994)

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