Lung cancer mortality in North Carolina and South Carolina chrysotile asbestos textile workers

Our plain-English summary of Lung cancer mortality in North Carolina and South Carolina chrysotile asbestos textile workers, by L. Elliott, D. Loomis, J. Dement, et al (Occupational and Environmental Medicine, 2012).

The study

• Authors: L. Elliott, D. Loomis, J. Dement, M.J. Hein, D. Richardson, L. Stayner
• Journal: Occupational and Environmental Medicine
• Published: 2012;69(6):385-90
• Cited by: 30 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: Studies of workers in two US cohorts of asbestos textile workers exposed to chrysotile (North Carolina (NC) and South Carolina (SC)) found increasing risk of lung cancer mortality with cumulative fibre exposure. However, the risk appeared to increase more steeply in SC, possibly due to differences in study methods. The authors conducted pooled analyses of the cohorts and investigated the exposure-disease relationship using uniform cohort inclusion criteria and statistical methods.

Methods: Workers were included after 30 days of employment in a production job during qualifying years, and vital status ascertained through 2003 (2001 for SC). Poisson regression was used to estimate the exposure-response relationship between asbestos and lung cancer, using both exponential and linear relative rate models adjusted for age, sex, race, birth cohort and decade of follow-up.

Results: The cohort included 6136 workers, contributing 218,631 person-years of observation and 3356 deaths. Cumulative exposures at the four study facilities varied considerably. The pooled relative rate for lung cancer, comparing 100 f-yr/ml to 0 f-yr/ml, was 1.11 (95% CI 1.06 to 1.16) for the combined cohort, with different effects in the NC cohort (RR=1.10, 95% CI 1.03 to 1.16) and the SC cohort (RR = 1.67, 95% CI 1.44 to 1.93).

Conclusions: Increased rates of lung cancer were significantly associated with cumulative fibre exposure overall and in both the Carolina asbestos-textile cohorts. Previously reported differences in exposure-response between the cohorts do not appear to be related to inclusion criteria or analytical methods.

In plain English

This study pooled two groups of US asbestos textile workers: 3082 from three North Carolina plants and 3054 from one South Carolina plant, 6136 in all, each employed at least 30 days in a production job. Most asbestos used was raw chrysotile; the South Carolina plant also used small amounts of crocidolite yarn, and one North Carolina plant some amosite. Deaths were followed through 2003 (2001 for South Carolina). Compared with national rates, the combined group had more deaths than expected from all causes (SMR 1.40, 95% CI 1.35 to 1.45) and from lung cancer (SMR 1.90, 95% CI 1.70 to 2.11). Lung cancer death rates rose with cumulative fiber exposure. Comparing 100 fiber-years/ml with none, the rate ratio was 1.11 (95% CI 1.06 to 1.16) for the combined cohort, 1.10 (1.03 to 1.16) for North Carolina and 1.67 (1.44 to 1.93) for South Carolina. The authors concluded that earlier differences between the two cohorts did not appear to come from inclusion rules or analysis methods, and that a single overall estimate may not be possible. They noted North Carolina records were less complete.

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: Pooled retrospective cohort mortality study of two previously studied cohorts. Mortality was compared with national rates (standardised mortality ratios), and exposure-response was estimated by Poisson regression.
• Who was studied: 6136 asbestos textile workers (3082 from North Carolina plants NC1, NC3 and NC4; 3054 from one South Carolina plant), contributing 218,630.8 person-years and 3356 deaths. Workers were included after 30 days in a production job during 1940 to 1965 (SC) or 1950 to 1973 (NC). Vital status was followed through 2001 (SC) and 2003 (NC). There were 361 lung cancer cases.
• Exposure: Mostly raw chrysotile used to make yarn and woven materials. There were also small amounts of crocidolite yarn in the SC plant (1950s to 1975) and some amosite in an insulation operation at NC3 (1963 to 1976). Cumulative exposure in fibre-years/ml was estimated from job exposure matrices, based on 3578 (NC) and 5952 (SC) industrial hygiene measurements. Mean cumulative exposure was 80.4 f-yr/ml in NC and 28.2 f-yr/ml in SC.
• Main results:
  • Combined cohort compared with the US national population: all-cause mortality SMR 1.40 (95% CI 1.35 to 1.45).
  • Combined cohort: lung cancer mortality SMR 1.90 (95% CI 1.70 to 2.11), significantly higher than expected.
  • Combined cohort: mesothelioma deaths SMR 8.61 (95% CI 1.78 to 25.17), based on only three deaths. Before 1999, mesothelioma deaths were likely coded as cancer of the pleura or other respiratory sites.
  • Combined cohort: the rate ratio for lung cancer comparing 100 f-yr/ml with 0 f-yr/ml was 1.11 (95% CI 1.06 to 1.16), as stated in the discussion. Table 2 lists 1.10 (1.06 to 1.15) for a 10-year lag.
  • North Carolina workers: rate ratio per 100 f-yr/ml 1.10 (95% CI 1.03 to 1.16), a weaker association than in South Carolina workers.
  • South Carolina workers: rate ratio per 100 f-yr/ml 1.67 (95% CI 1.44 to 1.93). The test for difference between cohorts gave p less than 0.0001.
  • By plant, only the NC3 and SC estimates were statistically significant. Table 2 gives NC3 1.14 (1.07 to 1.22), NC1 0.41 (0.12 to 1.34) and NC4 1.06 (0.93 to 1.21).
• The authors' conclusion: The authors concluded that lung cancer mortality increased significantly with asbestos exposure. They found that earlier differences between the NC and SC cohorts did not appear to be due to inclusion criteria or analytical methods. They suggested a single estimate of effect may not be possible. They proposed possible explanations: data quality, the healthy worker survivor effect, and differences in exposure distributions.
• Limitations the authors state:
  • About 7% of the cohort was lost to follow-up, and cause of death was unknown for about 5% of known deaths.
  • Occupational histories and exposure data for the NC plants were less complete, which could have caused exposure misclassification and weakened the exposure-response association.
  • A NC surveillance programme removed workers with x-ray changes from exposure. Workers who were dismissed or left may not have been enumerated, which could weaken the observed relationship.
  • The quality of cause-of-death coding on death certificates varies.

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: Lung Cancer, Chrysotile, Cumulative Exposure.

Related studies

• 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)
• 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 and fibre exposures among North Carolina asbestos textile workers — D. Loomis, J.M. Dement, et al. (2009)
• Estimates of historical exposures by phase contrast and transmission electron microscopy in North Carolina USA asbestos textile plants — J.M. Dement, D. Myers, et al. (2009)
• Follow-up study of chrysotile asbestos textile workers: cohort mortality and case-control analyses — J.M. Dement, D.P. Brown, et al. (1994)
• Cause-specific mortality in a Chinese chrysotile textile worker cohort — X. Wang, S. Lin, et al. (2013)

Browse more research in Occupational and Environmental Medicine, or return to medical research.