Asbestos Fiber Concentrations in the Lungs of Brake Repair Workers: An Updated Analysis Using Several Regression Methods to Handle Nondetectable Measurements

Our plain-English summary of Asbestos Fiber Concentrations in the Lungs of Brake Repair Workers: An Updated Analysis Using Several Regression Methods to Handle Nondetectable Measurements, by Y. Liu, G.M. Marsh, V.L. Roggli (Journal of Occupational and Environmental Medicine, 2018).

The study

• Authors: Y. Liu, G.M. Marsh, V.L. Roggli
• Journal: Journal of Occupational and Environmental Medicine
• Published: 2018;60(7):661-671
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: The aim of the study was to reanalyze an updated database of lung asbestos fiber levels for 21 brake repair workers who died of mesothelioma using robust maximum likelihood-based regression methods to address nondetectable measurements.

Methods: We applied bivariate normal regression to address the doubly left-censored situation where both the lung fiber concentration of noncommercial (TAA) and commercial amphiboles (AC) were subject to detection limits. For the single left-censored situation, we applied censored normal regression to study the relationship between duration of employment (DOE) and TAA.

Results: We found a statistically significant positive relationship between TAA and AC (β = 0.49, 95% confidence interval [CI], 0.11 to 0.86) and a not statistically significant relationship between DOE and TAA (β = 0.02, 95% CI, -0.03 to 0.06).

Conclusions: Our results provide additional support for the conclusion that exposure to commercial amphibole asbestos, and not chrysotile, is related to the occurrence of mesothelioma among some brake workers.

In plain English

This study reanalyzed lung-tissue fiber measurements from a case series of 21 brake repair workers who developed mesothelioma. For all of them, the only known or suspected asbestos exposure was contact with friction products. Lung levels of non-commercial amphiboles (tremolite, actinolite, anthophyllite) and commercial amphiboles (amosite, crocidolite) had been measured by electron microscopy. In 13 of the 21 workers (62%), one or both levels were below the detection limit. The authors therefore used statistical methods designed for such 'non-detects' and compared them with simpler substitution methods. On a log scale, lung levels of non-commercial amphiboles rose with lung levels of commercial amphiboles (slope 0.49, 95% CI 0.11 to 0.86). Non-commercial amphibole levels showed no statistically significant relationship with years worked as a brake worker (slope 0.02, 95% CI -0.03 to 0.06). The substitution methods gave consistent results. The authors concluded that the results support commercial amphibole exposure from some unrecognized source, and not chrysotile from friction products, as related to mesothelioma in these workers. They noted the very small sample, censoring of almost 50%, a case series that may not be representative, and possible recall bias.

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: Statistical reanalysis of an updated case series of lung-tissue fiber measurements, using maximum likelihood-based regression methods (bivariate normal regression and censored normal regression) compared with substitution methods for non-detectable measurements
• Who was studied: 21 brake repair workers who developed mesothelioma: cases 1-10 from the original analyses, cases 11-15 added in Marsh et al. (2011), and cases 16-21 added by one of the authors (VR) between 2011 and 2015
• Exposure: Contact with friction products was the only known or suspected asbestos exposure. Lung concentrations (fibers per gram) of non-commercial amphiboles (TAA: tremolite, actinolite, anthophyllite), commercial amphiboles (AC: amosite, crocidolite) and chrysotile were measured by scanning electron microscopy with energy dispersive x-ray analysis. Duration of employment as a brake worker was also studied.
• Main results:
  • Of the 21 workers, 8 (38%) had complete data for both amphibole lung concentrations, and 13 (62%) had one or both values below the detection limit (left-censored)
  • Bivariate normal regression: the slope between log-scale non-commercial amphibole and log-scale commercial amphibole lung concentrations was 0.49 (95% CI 0.11 to 0.86), statistically significantly different from zero (p = 0.006)
  • Simple linear regression with substituted values for non-detects: slopes between the two log-transformed fiber concentrations ranged from 0.53 to 0.57, and all were statistically significant
  • Censored normal regression: the slope between log-scale non-commercial amphibole lung concentration and duration of employment was 0.02 (95% CI -0.03 to 0.06), not statistically significantly different from zero (p = 0.47)
  • Sensitivity analysis excluding Cases 2 and 3 (potential outliers) gave a larger slope of 0.89 between the two log-scale amphibole concentrations (p = 0.0003)
  • The substitution methods and the maximum likelihood methods did not give inconsistent results
• The authors' conclusion: The authors concluded that the results support the conclusion that exposure to commercial amphibole asbestos from some unrecognized source, and not chrysotile derived from friction products, is related to the mesothelioma observed among the brake workers studied
• Limitations the authors state:
  • The sample size remains very small, at 21 brake workers
  • Censoring was almost 50% for both the outcome variable and the covariate
  • Few useful covariates were available for multiple imputation of censored observations
  • The analysis did not explicitly consider influential points with robust regression methods; a sensitivity analysis removing Cases 2 and 3 was done instead
  • The case series may not be representative of all people occupationally exposed to friction products
  • Exposure histories from patient interviews are subject to recall bias, which the authors say may explain the absence of reported commercial amphibole exposures

Topics

The National Library of Medicine indexes this study under subjects our site covers: Auto mechanics and brake work, Mesothelioma, Peritoneal mesothelioma, Tremolite.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Amphibole Group, confidence interval, Amphibole Asbestos, Chrysotile.

Related studies

• Asbestos fiber concentrations in the lungs of brake repair workers: commercial amphiboles levels are predictive of chrysotile levels — G.M. Marsh, A.O. Youk, et al. (2011)
• The analysis of asbestos count data with "nondetects": the example of asbestos fiber concentrations in the lungs of brake workers — M.M. Finkelstein (2013)
• Exposure to brake dust and malignant mesothelioma: a study of 10 cases with mineral fiber analyses — K.J. Butnor, T.A. Sporn, et al. (2003)
• Evaluation of asbestos exposure during brake repair and replacement — H. Kakooei, M. Hormozy, et al. (2011)
• Mesothelioma in a brake repair worker — A.M. Langer, W.T. McCaughey (1982)
• Personal exposures to asbestos fibers during brake maintenance of passenger vehicles — M.F. Cely-García, M. Sánchez, et al. (2012)

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