A historical cohort mortality study of workers exposed to asbestos in a refitting shipyard

Our plain-English summary of A historical cohort mortality study of workers exposed to asbestos in a refitting shipyard, by N. Kurumatani, Y. Natori, R. Mizutani, et al (Industrial Health, 1999).

The study

• Authors: N. Kurumatani, Y. Natori, R. Mizutani, S. Kumagai, M. Haruta, H. Miura, K. Yonemasu
• Journal: Industrial Health
• Published: 1999;37(1):9-17
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

To investigate the risks of developing asbestos-related diseases we conducted a historical cohort mortality study on 249 ship repair workers (90 laggers and 159 boiler repairers) in a single U.S. Navy shipyard in Japan. We successfully identified the vital status of 87 (96.7%) laggers and 150 (94.3%) boiler repairers, and, of these, 49 (56.3%) and 65 (43.3%) died, respectively, during the follow-up period from 1947 till the end of 1996. Our in-person interviews with some of the subjects clarified that asbestos exposure was considered to be substantially high in the 1950-60s, decreased thereafter gradually but remained till 1979 in the shipyard. The laggers, who had handled asbestos materials directly, showed a significantly elevated SMR of 2.75 (95% C.I.: 1.08-6.48) for lung cancer. The risk developing the disease was greater in the laggers after a 20-year latency (SMR = 3.42). Pancreatic cancer yielded a greater SMR than unity (7.78, 90% C.I.: 2.07-25.19) in a longer working years group. Four laggers died from asbestosis. The boiler repairers, who had many chances for secondary exposure to asbestos and a few for direct exposure, showed no elevation of the SMR of lung cancer overall, but there was a borderline statistically significant SMR of 2.41 (90% C.I.: 1.05-5.45) in a longer working years group. One boiler repairer died from mesothelioma and four from asbestosis.

In plain English

This historical cohort study followed 249 Japanese men employed from 1947 to 1979 as laggers (90) or boiler repairers (159) at a U.S. Navy ship repair yard in Japan. Their deaths through 1996 were compared with Japanese male death rates. Interviewed workers reported using mostly white asbestos, and the authors considered the fibers to be chrysotile and amosite, not crocidolite. Laggers (insulators), who handled asbestos directly, had five lung cancer deaths. That gave a standardized mortality ratio (SMR) of 2.75 (95% CI 1.08-6.48), or 3.42 (95% CI 1.35-8.08) when a 20-year latency was allowed. Four laggers died of asbestosis and none of mesothelioma. Pancreatic cancer was not significantly elevated among laggers overall, but in those who worked over 12 years its SMR was 7.78 (90% CI 2.07-25.19). Boiler repairers, exposed mostly indirectly, showed no statistically significant overall lung cancer excess. Those who worked over 15 years had a borderline SMR of 2.41 (90% CI 1.05-5.45). One boiler repairer died of pleural mesothelioma and four of asbestosis. The authors concluded that the lung cancer risk was causally associated with shipyard asbestos exposure. They noted that smoking could have contributed to a limited extent.

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: Historical (retrospective) cohort mortality study. Standardized mortality ratios (SMRs) were calculated against the Japanese male population, with in-person interviews of retired workers and of relatives of deceased workers.
• Who was studied: All 249 Japanese men employed as laggers (90) or boiler repairers (159) at any time from 1947 to the end of 1979 at a U.S. Navy refitting (ship repair) shipyard in Japan, after excluding 16 who left during the six-month apprenticeship. Follow-up ran from 1947 to the end of 1996.
• Exposure: Asbestos in ship repair work: insulating block, pipe sections, mattresses, cloth, felt, blankets and magnesia compound. The authors considered the fibers used to be chrysotile and amosite but not crocidolite. Laggers handled asbestos directly. Boiler repairers were exposed mainly indirectly, near laggers' work, with limited direct exposure. Exposure was described as high until the mid-1960s and declining thereafter, with countermeasures fully in place after 1979. No fiber measurements from this shipyard were published.
• Main results:
  • Laggers, all causes: 49 deaths, SMR 1.22 (95% CI 0.92-1.61).
  • Laggers, lung cancer: 5 deaths, SMR 2.75 (95% CI 1.08-6.48), significantly elevated.
  • Allowing a 20-year latency, the lung cancer SMR was 3.42 (95% CI 1.35-8.08) for laggers and 1.92 (0.66-4.94) for boiler repairers.
  • Laggers, non-malignant respiratory diseases, including four asbestosis deaths: statistically elevated SMR of 2.75.
  • Laggers, pancreatic cancer: two histologically verified cases. The SMR was not statistically elevated overall. In the longer working years group (over 12 years) the SMR was 7.78 (90% CI 2.07-25.19).
  • Boiler repairers, lung cancer: the overall SMR did not deviate statistically from the null value. In the longer working years group (over 15 years) there was a borderline statistically significant SMR of 2.41 (90% CI 1.05-5.45).
  • Boiler repairers: one died of malignant pleural mesothelioma and four of asbestosis. The SMRs for non-malignant respiratory disease, retroperitoneal tumor and pleural mesothelioma were statistically elevated.
  • Mesothelioma mortality was 0 per 100,000 person-years among laggers (0/2623) and 21.4 per 100,000 person-years among boiler repairers (1/4683). The authors described these rates as rather low compared with previous reports.
  • Of ten lung cancer deaths, hospital records were available for seven: two squamous cell carcinomas and five adenocarcinomas.
• The authors' conclusion: The authors concluded that the lung cancer risk observed among the study subjects is causally associated with asbestos exposure in the shipyard. On pancreatic cancer, they stated that further observations are required.
• Limitations the authors state:
  • The comparison group was an external population (Japanese males), and differing distributions of confounders between the groups could mislead conclusions.
  • Smoking was common (80.5% of laggers and 84.0% of boiler repairers had a smoking history). Differences in smoking could have contributed to the lung cancer SMRs, but to a limited extent.
  • Substitute national rates were used for asbestosis, pleural mesothelioma and retroperitoneal tumor, so these SMRs should be underestimated.
  • The small sample size made the mesothelioma results uncertain.
  • Average follow-up of about 30 years may not have been long enough to exceed the latent period for mesothelioma.
  • No asbestos fiber measurements were published for this shipyard. Exposure levels were estimated from U.S. Navy shipyard dust counts.
  • The site of the retroperitoneal tumor could not be specified because hospital records were unavailable.

Topics

Medical terms in this study, explained in our Lexicon: Insulator, Asbestos Exposure, Lung Cancer, Latency, Take-home Exposure, Mesothelioma.

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