Preliminary report on a prospective Mortality study of workers at an Asbestos Factory

Our plain-English summary of Preliminary report on a prospective Mortality study of workers at an Asbestos Factory, by M.L. Newhouse (1968).

The study

• Author: M.L. Newhouse
• Published: 2nd International Conference on the Biological Effects of Asbestos. April 22-26, 1968
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This preliminary report followed the deaths of men who started work between April 1933 and May 1948 at an asbestos factory in the East End of London that used crocidolite, chrysotile and amosite. Of 1335 men, 1226 (92 %) were traced to May 1964. Their deaths were compared with the numbers expected from England and Wales death rates. Jobs were graded 1 to 6 by dust exposure. The 520 men in grades 1 to 4 showed no significant excess of deaths. In severely exposed grade 5, deaths from cancer of the lung and pleura were 6 observed against 1.01 expected among men employed under 2 years, and 7 against 0.92 among men employed longer. In grade 6, longer-serving men had 4 against 0.62. Deaths from non-cancer respiratory disease were raised only in longer-serving grade 5 men: 9 against 1.81 expected, and 4 of the 9 were certified asbestotics. Review of autopsy reports and tissue reclassified 9 deaths as mesothelioma. The author concluded that a short heavy exposure appeared to carry an equal cancer risk to a long heavy exposure. The author noted that the pathology information was incomplete.

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: Preliminary report of a mortality study of a cohort of past male employees identified from the firm's personnel files. Observed deaths were compared with deaths expected from England and Wales death rates. Death-certificate diagnoses were checked against autopsy reports and histology where available.
• Who was studied: Men who started work at an asbestos factory in the East End of London between April 1933 and May 1948. All had completed one month's employment and survived at least 16 years from engagement. Follow-up ran to May 1964. There were 1335 men, of whom 1226 (92 %) were traced: 520 in exposure grades 1 to 4, 375 in grade 5 and 331 in grade 6.
• Exposure: Asbestos dust at a factory using crocidolite, chrysotile and amosite (particularly crocidolite in the early years), making textiles and insulation materials. Jobs were graded from 1 (office workers, very low exposure) to 6 (heavy exposure). Grade 4 was laggers, their mates and labourers. Grade 5 was chiefly makers of sectional insulating material, pipe covers and insulation slabs. Grade 6 was openers, disintegrators, textile workers and mattress makers. Men were also grouped by time employed: under 2 years, or 2 years or more.
• Main results:
  • Men in exposure grades 1 to 4 (520 men) had no significant excess of deaths, whether from all causes, all cancers, lung and pleura cancer, other cancers, or non-cancer respiratory disease.
  • Both severely exposed groups (grade 5 and grade 6) had a statistically significant excess of deaths from all causes. Among grade 5 men employed under 2 years there were 23 observed deaths against 11.09 expected (P less than 0.01).
  • Grade 5 men employed under 2 years: 6 deaths from cancer of the lung and pleura observed against 1.01 expected (P less than 0.001).
  • Men employed 2 years or more: 7 lung and pleura cancer deaths observed against 0.92 expected in grade 5 (P less than 0.001), and 4 observed against 0.62 expected in grade 6 (P less than 0.01). In grade 6 there was no excess of cancer deaths among men with short employment.
  • Grade 5 men employed under 2 years also had an excess of deaths from cancers other than lung and pleura. The text gives 7 observed against 1.72 expected (P less than 0.01); the table prints different figures.
  • Grade 5 men with long service: 9 deaths from respiratory disease excluding cancer, against 1.81 expected. Of the 9, 4 were certified asbestotics.
  • Grade 6 men had no excess mortality from respiratory disease (excluding cancer).
  • No occupational group had an excess of deaths from diseases other than cancers or respiratory disease.
  • Of 40 men certified as dying of cancer, further pathological information was available on 23.
  • Pathological review identified 9 additional mesothelial tumours among deaths certified as lung cancer, gastro-intestinal cancer or carcinomatosis. Of the 15 certified as lung or pleura cancer that were reviewed, 3 were revised to pleural mesothelioma.
  • With one further case for which no material was available, there were 10 mesothelial tumours in the series. Three of these men had been employed under two years. Two had worked in low or moderate exposure jobs and one was a lagger.
• The authors' conclusion: The author concluded that a short heavy exposure appeared to carry an equal cancer risk to a long heavy exposure, whereas death from respiratory disease without cancer appeared only after long and heavy exposure. The author also wrote that among workers in this factory the cancer risk seemed likely to be confined to cancer of the lung and mesothelioma of the pleura or peritoneum.
• Limitations the authors state:
  • Follow-up of men employed in the earlier years was incomplete, so observation in this report began in April 1933.
  • Pathological information was incomplete, particularly for men employed only for short periods.
  • Some death certificates could not be checked against pathology and may conceal misdiagnosed mesothelial tumours.
  • For one case recorded as peritoneal mesothelioma, no material was available to confirm the diagnosis.

Topics

Medical terms in this study, explained in our Lexicon: Crocidolite, Chrysotile, Amosite, Pleura, Autopsy, Mesothelioma, Pathology.

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