Historical cohort study of a New Zealand foundry and heavy engineering plant

Our plain-English summary of Historical cohort study of a New Zealand foundry and heavy engineering plant, by H.M. Firth, J.M. Elwood, B. Cox, et al (Occupational and Environmental Medicine, 1999).

The study

• Authors: H.M. Firth, J.M. Elwood, B. Cox, G.P. Herbison
• Journal: Occupational and Environmental Medicine
• Published: 1999;56(2):134-8
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To investigate the mortality of workers who had been exposed to asbestos, machining fluids and foundry work in a foundry and heavy engineering plant in the railway rolling stock manufacturing industry in New Zealand.

Methods: Historical cohort study design.

Results: For the total workforce of 3522 men employed between 1945 and 1991, follow up was 90% of person-years to 31 December 1991. Significantly increased standardised mortality ratios (SMRs) were found for all causes of death combined (SMR 1.07; 95% confidence interval (95% CI) 1.01 to 1.14), all malignancies (SMR 1.15; 95% CI 1.01 to 1.31), circulatory (SMR 1.16; 95% CI 1.07 to 1.27) and musculoskeletal diseases (SMR 3.06; 95% CI 1.39 to 5.84), all digestive cancers (SMR 1.29; 95% CI 1.04 to 1.59), all respiratory cancers (SMR 1.34; 95% CI 1.08 to 1.65), cancer of the oesophagus (SMR 1.97; 95% CI 1.01 to 3.45), and mesothelioma of the pleura (SMR 6.58; 95% CI 1.24 to 19.49). Three deaths from pleural mesothelioma were recorded, with latency times of 51, 53, and 57 years. There were no dose-response relations between exposure to asbestos, machining fluids or foundry work, or by duration of employment in the plant, and any cause of death.

Conclusions: This study found small increases in risk for several causes of death among foundry and heavy engineering workers; however, these increases were small and the possible effects of smoking and other lifestyle factors could not be excluded. There was evidence of asbestos related disease in those involved in engineering work in the past.

In plain English

This historical cohort study followed 3522 men who had worked for more than three months between 1945 and 1991 at a New Zealand plant that built and repaired railway rolling stock. The asbestos used to insulate steam engines was chrysotile. The whole workforce had more deaths than expected from all causes (standardised mortality ratio, SMR 1.07; 95% CI 1.01 to 1.14) and from all respiratory cancers (SMR 1.34; 95% CI 1.08 to 1.65). Lung cancer was raised but not statistically significant (SMR 1.25; 95% CI 0.99 to 1.56). Three men died of pleural mesothelioma (SMR 6.58; 95% CI 1.24 to 19.49). All three were first employed in the 1920s, and their latency times were 51, 53 and 57 years. There were no peritoneal mesothelioma deaths. Risk did not rise with estimated asbestos exposure. Smoking habits were unknown. The authors concluded that the increases were small, that smoking and lifestyle could not be excluded as explanations, and that there was evidence of asbestos-related disease among past engineering workers.

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 cohort study (mortality compared with New Zealand men using standardised mortality ratios)
• Who was studied: Men who worked more than 3 months between 1945 and 1991 at a New Zealand foundry and heavy engineering plant making and repairing railway rolling stock; followed to 31 December 1991
• Exposure: Chrysotile asbestos (stripping and re-insulating steam engine boilers; boilermakers and holder-uppers most exposed), machining fluids (mineral oils) and foundry work; exposure estimated from job title, with no measurements
• Main results:
  • Of the 3522 men, 57.9% were known to be alive and 28.3% had died by the end of 1991
  • Total workforce, all causes of death: 996 observed vs 929.76 expected, SMR 1.07 (95% CI 1.01 to 1.14)
  • Total workforce, all respiratory cancers: 88 observed vs 65.62 expected, SMR 1.34 (95% CI 1.08 to 1.65)
  • Total workforce, lung cancer: 78 observed vs 62.57 expected, SMR 1.25 (95% CI 0.99 to 1.56), increased but not statistically significant
  • Total workforce, pleural mesothelioma: 3 observed vs 0.46 expected, SMR 6.58 (95% CI 1.24 to 19.49)
  • The three pleural mesothelioma deaths were in men first employed in the 1920s in their teens who worked at the plant for more than 40 years; latency times were 57, 53 and 51 years
  • No deaths from peritoneal mesothelioma
  • Crude pleural mesothelioma mortality among those with any asbestos exposure was 0.87 per 1000 men
  • One death was recorded as due to asbestosis, and three other men had lung fibrosis or interstitial lung disease as a contributing cause; all four worked in insulating areas
  • No trend of increasing risk for any cause of death with increasing exposure to asbestos, machining fluids or foundry work
  • Labourers (mixed exposure group) had an increased lung cancer SMR of 1.74 (95% CI 1.18 to 2.48)
  • SMRs for all causes and lung cancer decreased with longer employment, which the authors saw as a selection effect
• The authors' conclusion: The authors concluded that risk was increased for several causes of death, but the increases were small and smoking and other lifestyle factors could not be excluded; there was evidence of asbestos-related disease among past engineering workers.
• Limitations the authors state:
  • Smoking prevalence in the cohort was unknown
  • No data on past exposure; no environmental measurements had ever been made at the plant
  • Classifying men by their longest-held job may have underestimated exposure
  • Pleural mesothelioma is underreported, so more mesothelioma deaths probably occurred than were recorded
  • Some selection bias may remain despite 90% person-year follow-up

Topics

Medical terms in this study, explained in our Lexicon: Cohort Study, confidence interval, Mesothelioma, Pleura, Pleural Mesothelioma, Latency, Dose-response relationship.

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