Nested case-control study of autoimmune disease in an asbestos-exposed population

Our plain-English summary of Nested case-control study of autoimmune disease in an asbestos-exposed population, by C.W. Noonan, J.C. Pfau, T.C. Larson, et al (Environmental Health Perspectives, 2006).

The study

• Authors: C.W. Noonan, J.C. Pfau, T.C. Larson, M.R. Spence
• Journal: Environmental Health Perspectives
• Published: 2006;114(8):1243-7
• Type of article: Randomized trial
• Cited by: 92 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objective: To explore the potential association between asbestos exposure and risk of autoimmune disease, we conducted a case-control study among a cohort of 7,307 current and former residents of Libby, Montana, a community with historical occupational and environmental exposure to asbestos-contaminated vermiculite.

Methods: Cases were defined as those who reported having one of three systemic autoimmune diseases (SAIDs): systemic lupus erythematosus, scleroderma, or rheumatoid arthritis (RA). Controls were randomly selected at a 3:1 ratio from among the remaining 6,813 screening participants using frequency-matched age and sex groupings.

Results: The odds ratios (ORs) and 95% confidence intervals (CIs) for SAIDs among those >or=65 years of age who had worked for the vermiculite mining company were 2.14 (95% CI, 0.90-5.10) for all SAIDs and 3.23 (95% CI, 1.31-7.96) for RA. In this age group, exposure to asbestos while in the military was also an independent risk factor, resulting in a tripling in risk. Other measures of occupational exposure to vermiculite indicated 54% and 65% increased risk for SAIDs and RA, respectively. Those who had reported frequent contact with vermiculite through various exposure pathways also demonstrated elevated risk for SAIDs and RA. We found increasing risk estimates for SAIDs with increasing numbers of reported vermiculite exposure pathways (p<0.001).

Conclusion: These preliminary findings support the hypothesis that asbestos exposure is associated with autoimmune disease. Refined measurements of asbestos exposure and SAID status among this cohort will help to further clarify the relationship between these variables.

In plain English

This nested case-control study examined whether exposure to asbestos-contaminated vermiculite was associated with three systemic autoimmune diseases: rheumatoid arthritis, lupus and scleroderma. It drew on 7,307 current and former residents of Libby, Montana, screened in 2000–2001. Of these, 494 reported ever having one of the diseases, and 1,482 controls from matching age and sex groups were selected from the rest. In a follow-up mailing, 161 of the 208 who replied confirmed a physician diagnosis, 129 of them rheumatoid arthritis. Overall, past work for the mining company W.R. Grace/Zonolite showed no increase (odds ratio 1.03; 95% CI 0.69–1.58). Among participants aged 65 or older who had worked there, the odds ratio for rheumatoid arthritis was 3.23 (95% CI 1.31–7.96). Dust or vermiculite exposure at other jobs, gardening with vermiculite and frequently playing in vermiculite piles were linked to higher odds. Odds rose with the number of exposure pathways reported. The authors concluded that these preliminary findings support the hypothesis that asbestos exposure is associated with autoimmune disease. They noted that both disease and exposure were self-reported, so recall bias and biased case finding were possible.

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: Nested case-control study within a community health screening cohort
• Who was studied: 7,307 current and former residents of Libby, Montana, who took part in the ATSDR screening program in 2000–2001. Cases were 494 participants who answered yes to 'Have you ever had rheumatoid arthritis, scleroderma, or lupus?' Controls were 1,482 participants who answered no, randomly selected within sex and 10-year age groups at a 3:1 ratio. In a follow-up mailing, 161 participants confirmed a physician diagnosis: 129 rheumatoid arthritis (RA), 30 systemic lupus erythematosus (SLE) and 4 scleroderma (SSc).
• Exposure: Asbestos-contaminated vermiculite from the Libby mine, plus other asbestos exposures. Exposure was taken from self-reported occupational, residential and recreational histories. Pathways included working for W.R. Grace/Zonolite, contract work, living with workers, dust or vermiculite at other jobs, asbestos exposure in the military, other asbestos trades, gardening with vermiculite, playing in vermiculite piles, recreating near Rainey Creek Road and 'popping' vermiculite.
• Main results:
  • Of the 494 initial cases sent the follow-up questionnaire, 208 responded. Of these, 161 confirmed a physician-diagnosed systemic autoimmune disease.
  • Overall, previous work with the mining company was not associated with increased risk of any of the three diseases combined (OR 1.03; 95% CI 0.69–1.58).
  • For participants aged 65 or older who ever worked for W.R. Grace/Zonolite, adjusted odds ratios were: 1.47 (0.82–2.63) for the original 494 self-reported cases; 2.14 (0.90–5.10) for the 161 physician-confirmed cases; and 3.23 (1.31–7.96) for the 129 RA cases.
  • Dust or vermiculite exposure at jobs other than W.R. Grace/Zonolite had adjusted odds ratios of: 1.33 (1.08–1.64) for the original 494 cases; 1.54 (1.10–2.15) for the 161 confirmed cases; and 1.65 (1.14–2.39) for RA.
  • In the final age-stratified models for participants aged 65 or older, asbestos exposure in the military had an odds ratio of 2.99 (1.04–8.59) for any confirmed disease and 3.31 (1.00–10.96) for RA.
  • Using vermiculite for gardening had adjusted odds ratios of: 1.31 (1.06–1.62) for the original 494 cases; 1.70 (1.19–2.43) for the 161 confirmed cases; and 1.70 (1.15–2.53) for RA.
  • Frequently playing in the vermiculite piles had adjusted odds ratios of: 1.39 (1.02–1.91) for the original 494 cases; 1.85 (1.18–2.92) for the 161 confirmed cases; and 2.06 (1.27–3.34) for RA.
  • Odds rose with the number of exposure pathways (trend p less than 0.001 for confirmed cases and for RA). For 6 or more pathways compared with none, the adjusted OR was 2.58 (0.60–11.05) for confirmed cases (96 cases out of 637 controls) and 3.98 (0.53–29.66) for RA (80 cases out of 637 controls).
  • SLE, with 30 cases, was too few to test for trend. Odds of SLE were higher among those with more than three exposure pathways than among those with three or fewer (OR 4.45; 95% CI 1.24–16.00).
  • Reported autoimmune disease was associated with parenchymal abnormalities on chest radiographs and with restrictive spirometry, but not strongly with pleural abnormalities.
• The authors' conclusion: The authors concluded that their preliminary findings support the hypothesis that asbestos exposure is associated with autoimmune disease. They said the results warrant a more comprehensive study with improved disease and exposure characterization.
• Limitations the authors state:
  • Exposure pathways of unequal intensity and duration were combined.
  • Cases were self-reported. Almost 23% of those who answered the mailing could not confirm their disease, and even the confirmed cases rest on self-report.
  • Case finding may have been biased by exposure: more heavily exposed people may have received more medical care and been more likely to be diagnosed.
  • Controls were not confirmed to be free of disease.
  • Exposure was self-reported, so exposure misclassification and recall bias are possible.
  • The time order of asbestos exposure, autoimmune response and asbestos-related disease was outside the study's scope.
  • There were too few scleroderma cases to analyze by exposure pathway.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Libby vermiculite mine, Montana

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Talc and vermiculite.

Medical terms in this study, explained in our Lexicon: nested case-control study, Asbestos Exposure, Case-Control Study, Environmental Exposure, vermiculite, Odds Ratio, confidence interval, Occupational Exposure.

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