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Continued increase in prevalence of r-type opacities among underground coal miners in the USA
  1. Noemi B Hall,
  2. David J Blackley,
  3. Cara N Halldin,
  4. A Scott Laney
  1. Respiratory Health Division, National Institute for Occupational Safety and Health, Morgantown, West Virginia, USA
  1. Correspondence to Dr Noemi B Hall, Respiratory Health Division, National Institute of Occupational Safety and Health, Morgantown, WV 26505–2888, USA; nhall{at}


Introduction Respirable crystalline silica exposure has been implicated in the resurgence of coal workers’ pneumoconiosis (CWP) in the USA. A 2010 report found an increasing prevalence of r-type opacities, which are associated with silicosis lung pathology, on the radiographs of working underground coal miners in central Appalachia. This analysis updates that report by assessing the prevalence of r-type opacities during 2010–2018 compared with earlier decades.

Methods Data from the Coal Workers’ Health Surveillance Program were used to calculate the prevalence of r-type opacities on radiographs of working underground coal miners. The data were restricted to radiographs taken during 1 January 1980 to 15 September 2018. The presence of r-type opacities was defined as an r-type classification for either the primary or secondary shape/size of small opacities. Prevalence ratios for r-type opacities were calculated using log binomial regression.

Results Radiograph classifications for 106 506 miners were included in analysis. For the USA overall, the prevalence of r-type opacities among miners with radiographs taken during 2010–2018 compared with 1980–1989 has increased (PR 2.4; 95% CI 1.9 to 3.0). For central Appalachia, the proportion of r-type opacities observed increased when comparing 1980–1989 to 2010–2018 (PR 6.0; 95% CI 4.6 to 7.9).

Conclusions The prevalence of r-type opacities on the radiographs of Appalachian underground coal miners continues to increase, implicating exposure to crystalline silica in respirable coal mine dust. The current findings underscore the importance of monitoring and controlling exposure to silica in coal mines.

  • epidemiology
  • pneumoconioses
  • silicosis
  • health surveillance
  • coal dust

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  • Contributors NBH: analysed and interpreted the data, led writing of the article and takes responsibility for its content. DJB and CNH: assisted with interpreting data and writing the article. ASL: conceptualised and designed the study and helped with data interpretation and writing.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Ethics approval CWHSP is a public health surveillance programme with non-research designation and is exempt from NIOSH Human Subjects Review Board approval (11-DRDS-NR03).

  • Provenance and peer review Not commissioned; externally peer reviewed.