Pneumoconiosis among underground bituminous coal miners in the United States: is silicosis becoming more frequent?

Abstract

Objectives: Epidemiologic reports since 2000 have documented increased prevalence and rapid progression of pneumoconiosis among underground coal miners in the United States. To investigate a possible role of silica exposure in the increase, we examined chest x-rays (CXRs) for specific abnormalities (r-type small opacities) known to be associated with silicosis lung pathology.

Methods: Underground coal miners are offered CXRs every 5 years. Abnormalities consistent with pneumoconiosis are recorded by National Institute for Occupational Safety and Health (NIOSH) B Readers using the International Labour Office Classification of Radiographs of Pneumoconioses. CXRs from 1980–2008 of 90,973 participating miners were studied, focusing on reporting of r-type opacities (small rounded opacities 3–10 mm in diameter). Log binomial regression was used to calculate prevalence ratios adjusted for miner age and profusion category.

Results: Among miners from Kentucky, Virginia, and West Virginia, the proportion of radiographs showing r-type opacities increased in the 1990s (PR=2.5; 95% CI=1.7–3.7) and after 1999 (PR=4.1; 95% CI=3.0–5.6), compared to the 1980s (adjusted for profusion category and miner age). The prevalence of progressive massive fibrosis in 2000-2008 was also elevated compared to the 1980’s (PR=4.4; 95% CI=3.1–6.3) and 1990’s (PR=3.8; 95% CI=2.1–6.8) in miners from Kentucky, Virginia, and West Virginia.

Conclusions: The increasing prevalence of pneumoconiosis over the past decade and the change in the epidemiology and disease profile documented in this and other recent studies imply that U.S. coal miners are being exposed to excessive amounts of respirable crystalline silica.