Case-fatality study of workers and residents with radiographic asbestos disease in Libby, Montana

Our plain-English summary of Case-fatality study of workers and residents with radiographic asbestos disease in Libby, Montana, by A. Miller, C.B. Black, G. Loewen, et al (American Journal of Industrial Medicine, 2022).

The study

• Authors: A. Miller, C.B. Black, G. Loewen, C.W. Noonan, T. McNew, A.C. Whitehouse, A.L. Frank
• Journal: American Journal of Industrial Medicine
• Published: 2022;65(3):196-202
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Vermiculite ore from Libby, Montana contains on average 24% of a mixture of toxic and carcinogenic amphibole asbestiform fibers. These comprise primarily winchite (84%), with smaller quantities of richterite (11%) and tremolite (6%), which are together referred to as Libby amphibole (LA).

Methods: A total of 1883 individuals who were occupationally and/or environmentally exposed to LA and were diagnosed with asbestos-related pleuropulmonary disease (ARPPD) following participation in communitywide screening programs supported by the Agency for Toxic Substances and Disease Registry (ATSDR) and followed up at the Center for Asbestos Related Disease (CARD) between 2000 and 2010. There were 203 deaths of patients with sufficient records and radiographs. Best clinical and radiologic evidence was used to determine the cause of death, which was compared with death certificates.

Results: Asbestos-related mortality was 55% (n = 112) in this series of 203 patients. Of the 203 deaths, 34 (17%) were from asbestos-related malignancy, 75 (37%) were from parenchymal asbestosis, often with pleural fibrosis, and 3 (1.5%) were from respiratory failure secondary to pleural thickening.

Conclusions: Asbestos is the leading cause of mortality following both occupational and nonoccupational exposure to LA in those with asbestos-related disease.

© 2021 The Authors. American Journal of Industrial Medicine Published by Wiley Periodicals LLC.

In plain English

This case-fatality study examined 203 people who died by February 22, 2010. All had been diagnosed with asbestos-related pleuropulmonary disease at the Center for Asbestos Related Disease in Libby, Montana. Of 237 reported deaths, 20 were excluded for unobtainable death certificates and 14 for insufficient medical records. People were exposed to Libby amphibole (winchite, richterite and tremolite) at work (103 mine, processing or lumber mill workers) or outside work (100 family members and community residents). Exposure was not measured. Death certificates, records, radiographs and lung function were reviewed. They classed 112 of 203 deaths (55%) as asbestos-related: 78 from asbestosis or asbestos-related pleural fibrosis and 34 from asbestos-related cancers (4 mesotheliomas, 26 lung, 1 laryngeal, 3 ovarian). Of the 78 non-cancer asbestos deaths, 33 death certificates omitted asbestosis. Among people exposed outside work, 47 of 100 deaths were asbestos-related. Three deaths came from pleural thickening without significant interstitial disease. The authors concluded asbestos is a principal cause of death after Libby amphibole exposure, at work and elsewhere. They noted the clinic may have attracted people with more symptoms.

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: Case-fatality study (series of deaths) with cause of death assigned by review of death certificates, medical records, radiographs and lung function ('best evidence')
• Who was studied: 203 deceased patients diagnosed with asbestos-related pleuropulmonary disease (ARPPD) at CARD, Libby, Montana. All were seen between July 1, 2000 and February 22, 2010 and died by February 22, 2010. Of 237 reported deaths, 20 were excluded because death certificates were unobtainable and 14 because medical records were insufficient.
• Exposure: Libby amphibole (LA). Exposure was classed as occupational (mine and mine-related workers or lumber mill workers) or nonoccupational (families of workers and community members exposed while living in Libby). Exposure was not quantified.
• Main results:
  • Of all 203 deaths, 112 (55%) were classed as asbestos-related.
  • Of the 203 deaths, 77 were asbestos-related according to the death certificate and were confirmed by chart review and chest radiography.
  • A further 35 deaths were judged asbestos-related from best evidence, based on medical records and radiograph review.
  • Of the 112 asbestos-related deaths, 78 were from asbestosis or asbestos-related pleural fibrosis and 34 were from asbestos-related cancers.
  • The 34 asbestos-related cancer deaths comprised 4 mesotheliomas, 26 lung cancers, 1 laryngeal cancer and 3 ovarian cancers.
  • Of the 78 non-cancer asbestos-related deaths, 45 had asbestosis noted on the death certificate and 33 did not.
  • Asbestos-related cancer accounted for 20% of deaths among current or former smokers and 7% among nonsmokers. Asbestosis/pleural fibrosis accounted for 38% and 39% respectively.
  • The occupational group had 103 deaths and the nonoccupational group had 100.
  • A larger share of deaths was attributed to non-asbestos disease in the nonoccupationally exposed group than in the occupationally exposed group (53% vs. 37%).
  • Among the 100 deaths in the nonoccupationally exposed group, 47 were asbestos-related.
  • 75 of the 78 non-cancer asbestos-related deaths involved a mixture of interstitial pulmonary fibrosis (asbestosis) and pleural fibrosis.
  • Three deaths were from pleural thickening without significant interstitial disease: 2 from lamellar pleural thickening and 1 from extensive circumscribed pleural thickening.
• The authors' conclusion: The authors concluded that asbestos is a principal cause of death for people exposed to the Libby amphibole mixture of winchite, richterite and tremolite, in both occupational and nonoccupational settings.
• Limitations the authors state:
  • CARD was the only pulmonary specialty clinic within 80 miles, so it may have attracted patients more likely to have lung symptoms. Asymptomatic patients with minimal disease may have been less likely to be included.
  • Screening relied on plain chest radiographs, which easily miss the subtle pleural disease seen in these patients. The 1883 diagnosed cases are therefore likely an underestimate.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: vermiculite, Carcinogenic, Amphibole Group, Asbestiform, winchite, richterite, Tremolite, Libby amphiboles.

Related studies

• Asbestos-related pleural disease due to tremolite associated with progressive loss of lung function: serial observations in 123 miners, family members, and residents of Libby, Montana — A.C. Whitehouse (2004)
• Radiographic abnormalities and exposure to asbestos-contaminated vermiculite in the community of Libby, Montana, USA — L.A. Peipins, M. Lewin, et al. (2003)
• Radiographic abnormalities and asbestos exposure: Libby, Montana — B. Price (2004)
• Workers with Libby amphibole exposure: retrospective identification and progression of radiographic changes — T.C. Larson, C.A. Meyer, et al. (2010)
• A clinical evaluation and tissue fiber burden analysis of a lifetime resident of Libby, Montana with adenocarcinoma of the lung — R.F. Dodson, B. Black, et al. (2020)
• Libby Amphibole Disease: Pulmonary Function and CT Abnormalities in Vermiculite Miners — A. Miller, J. Szeinuk, et al. (2018)

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