Follow-up study of chrysotile asbestos textile workers: cohort mortality and case-control analyses

Our plain-English summary of Follow-up study of chrysotile asbestos textile workers: cohort mortality and case-control analyses, by J.M. Dement, D.P. Brown, A. Okun (American Journal of Industrial Medicine, 1994).

The study

• Authors: J.M. Dement, D.P. Brown, A. Okun
• Journal: American Journal of Industrial Medicine
• Published: 1994;26(4):431-47
• Cited by: 102 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Previous studies of mortality among white males employed in a Charleston, South Carolina asbestos textile plant using chrysotile demonstrated significant excess mortality due to asbestos-related disease and a steep exposure-response relationship for lung cancer. This cohort was further studied by adding 15 years of follow-up and including mortality among white female and black male workers. Nested case-control analyses were undertaken to further explore possible differences in lung cancer risk by textile operation as well as possible confounding by mineral oil exposures. Preliminary data for white males have been previously published. White males experienced statistically significant excess mortality due to lung cancer (standardized mortality ratio [SMR] = 2.30; confidence interval [CI] = 1.88-2.79), all causes (SMR = 1.48; CI = 1.38-158), all cancers (SMR = 1.50; CI = 1.29-1.72), diabetes mellitus (SMR = 2.05; CI = 1.18-3.33), heart disease (SMR = 1.41; CI = 1.26-1.58), cerebrovascular disease (SMR = 1.50; CI = 1.08-2.02), pneumoconiosis and other respiratory diseases (SMR = 4.10; CI = 3.10-5.31), and accidents (SMR = 1.49; CI = 1.15-1.91). Among white females, statistically significant excesses occurred for lung cancer (SMR = 2.75; CI = 2.06-3.61), all causes (SMR = 1.21; CI = 1.11-1.32), pneumoconiosis and other respiratory diseases (SMR = 2.40; CI = 1.53-3.60), and other respiratory cancers (SMR = 14.98; CI = 4.08-38.7). Among the total cohort of black males, the only statistically significant excess observed was for pneumoconiosis (SMR = 2.19; CI = 1.23-3.62). Based on historical exposure measurements at the plant, there was a positive exposure-response relationship for both lung cancer and pneumoconiosis. Data for the entire cohort demonstrate an increase in the lung cancer relative risk of 2-3% for each fiber/cc-year of cumulative chrysotile exposure. This relationship was more consistent for the white male workers. The excess risk for lung cancer among white males and females appeared to occur at cumulative exposures lower than those for black males. Possible reasons for the lesser lung cancer risk among black males include less smoking and differences in airborne fiber characteristics experienced by black males as a result of plant job placement patterns. The case-control analysis found employment in preparation and carding operations (where most of the black males worked) to be associated with a slightly reduced lung cancer risk, although not statistically significant, whereas spinning and twisting employment was associated with a statistically significant increased lung cancer risk compared to other plant operations.(ABSTRACT TRUNCATED AT 400 WORDS)

In plain English

This study extended follow-up of workers at a South Carolina chrysotile asbestos textile plant by 15 years, to 1990, adding white women and black men. The 3,022 workers had at least one month in textile production operations between 1940 and 1965. Against U.S. rates, white men had 2.30 times expected lung cancer deaths (90% confidence interval 1.88-2.79) and 4.10 times expected deaths from pneumoconiosis and other respiratory diseases (3.10-5.31). White women had 2.75 times expected lung cancer deaths (2.06-3.61). Black men overall had fewer lung cancer deaths than expected (0.78; 0.47-1.22; not significant), though the highest-exposure group showed a significant excess. Their excess for pneumoconiosis and other respiratory diseases (2.19; 1.23-3.62) was significant, as was a broader respiratory disease category (1.47; 1.02-2.05). Whole-cohort lung cancer relative risk rose about 2% per fiber/cc-year of cumulative exposure. In a case-control analysis, longest work in spinning and twisting was linked to higher lung cancer risk, and mineral oil had little effect on the asbestos exposure-response estimates. Mesothelioma appeared on two white men's death certificates. The authors suggested less smoking and fiber differences might explain black men's lower risk.

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 an earlier study), with a nested case-control analysis of lung cancer
• Who was studied: 3,022 workers at a South Carolina asbestos textile plant: 1,247 white males, 1,229 white females and 546 black males. All were employed in the textile production operations for at least 1 month between January 1, 1940 and December 31, 1965, with vital status followed through December 31, 1990. The case-control analysis used 126 lung cancer deaths (74 white males, 38 white females, 14 nonwhite males), with five matched controls for each.
• Exposure: Chrysotile asbestos was the only asbestos type processed as raw fiber. Crocidolite yarn was used in small quantities (about 2,000 pounds in total) from the 1950s until 1975 and was never carded, spun or twisted. Cumulative exposure was estimated in fibers longer than 5 micrometers per cc, by job and calendar year. Mineral oil exposure was also examined as a possible confounder.
• Main results:
  • White males: lung cancer SMR 2.30 (90% CI 1.88-2.79), based on U.S. rates.
  • White males: pneumoconiosis and other respiratory diseases SMR 4.10 (90% CI 3.10-5.31). About 50% (21/41) of these deaths were due to pneumoconiosis.
  • White females: lung cancer SMR 2.75 (90% CI 2.06-3.61). Pneumoconiosis and other respiratory diseases SMR 2.40 (90% CI 1.53-3.60).
  • Black males: overall lung cancer SMR 0.78 (90% CI 0.47-1.22), which was not statistically significant.
  • Black males: a statistically significant lung cancer excess occurred only at the highest cumulative exposure, although data in the low exposure stratum were sparse.
  • Black males overall: pneumoconiosis and other respiratory diseases SMR 2.19 (90% CI 1.23-3.62), statistically significant.
  • Black males overall: in Table III, the broader respiratory disease category (which includes pneumoconiosis and other respiratory diseases) had SMR 1.47 (90% CI 1.02-2.05).
  • Black males: a statistically significant lung cancer deficit below 40,000 fiber/cc-days (SMR 0.40; 6 observed vs. 14.8 expected).
  • Lung cancer trend with cumulative exposure: statistically significant for white males (Z = 2.88; p less than 0.01) but not for white females (Z = 1.71; p greater than 0.05).
  • Lung cancer relative risk rose about 3% per fiber/cc-year for white males, 1% for white females and 2% for the whole cohort. A weighted regression on the whole-cohort SMR data gave a 3% increase per fiber/cc-year.
  • Pneumoconiosis: a positive exposure-response was seen in all race/sex groups.
  • Case-control analysis, compared with under 1,000 fiber/cc-days: the lung cancer odds ratio was 7.11 (95% CI 3.51-14.40) at 40,000 fiber/cc-days or more. With control for mineral oil it was 7.03 (3.47-14.24).
  • Mineral oil exposure had little effect on the lung cancer exposure-response estimates for asbestos.
  • Longest employment in spinning and twisting was associated with increased lung cancer risk compared with other plant operations (OR 1.75, 95% CI 1.07-2.86). Odds ratios for preparation (0.88) and carding (0.80) were not statistically different from 1.0.
  • Mesothelioma was recorded on the death certificates of two white males, both primarily employed in spinning, with latency periods of 37 and 34 years.
• The authors' conclusion: The authors concluded that the results for white males confirm the original study's findings. They suggested that reduced smoking and differences in airborne fiber characteristics might partially explain the lower lung cancer risk among black males, most of whom worked in preparation and carding.
• Limitations the authors state:
  • Follow-up was less complete for females: 22.8% of white females had unknown vital status.
  • Because of losses to follow-up, the authors placed more confidence and emphasis on the exposure-response analysis for white males.
  • Few lung cancer deaths among black males at low exposure made it difficult to look at differences by race.
  • Smoking patterns compared with U.S. reference rates may have led to underestimating lung cancer risk for black males and overestimating it for white females.
  • The fiber size samples came from 1965-1971 and may not represent earlier fiber characteristics.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Lung Cancer, Confounding, standardized mortality ratio (SMR), confidence interval, Pneumoconiosis, Relative Risk, Cumulative Exposure.

Related studies

• Cause-specific mortality in a Chinese chrysotile textile worker cohort — X. Wang, S. Lin, et al. (2013)
• Lung cancer mortality in North Carolina and South Carolina chrysotile asbestos textile workers — L. Elliott, D. Loomis, et al. (2012)
• Increased lung cancer mortality among chrysotile asbestos textile workers is more strongly associated with exposure to long thin fibres — D. Loomis, J.M. Dement, et al. (2012)
• Lung cancer mortality among asbestos textile workers: a review and update — J.M. Dement, D.P. Brown (1994)
• Cancer mortality among Chinese chrysotile asbestos textile workers — X.R. Wang, I.T. Yu, et al. (2012)
• Estimates of historical exposures by phase contrast and transmission electron microscopy for pooled exposure--response analyses of North Carolina and South Carolina, USA asbestos textile cohorts — J.M. Dement, D. Loomis, et al. (2011)

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