Objective To assess whether the recent increases in the prevalence of coal workers' pneumoconiosis (CWP) in the USA reflect increased measured exposures over recent decades, and to identify other potential causative factors.

Methods The observed CWP prevalence was calculated for 12 408 underground coal miner participants in the Coal Workers' Health Surveillance Program for the period 2005–2009, stratified by the Mine Safety and Health Administration (MSHA) geographical districts. The predicted prevalence was estimated using a published exposure–response model from a large epidemiological study among US coal miners using dust exposure, tenure, miner's age and coal rank as predictors. χ² Testing was performed to compare the observed versus predicted CWP prevalence.

Results Observed prevalence was significantly higher than predicted prevalence in MSHA districts 4–7 (central Appalachian region) (10.1% vs 4.2%; prevalence ratio (PR) 2.4; p<0.001) and significantly lower than predicted in other regions (1.6% vs 3.6%; PR 0.4; p<0.001). The central Appalachian region had a significantly older workforce with greater mining tenure, a lower proportion of mines with 200 or more employees, and lower seam heights. Significant lower average compliance dust concentrations were reported for this region.

Conclusion The observed CWP prevalence substantially exceeded predicted levels in central Appalachia. However, the increased prevalence was not explained by the measured levels of dust exposures. Likely contributing factors include mine size and low seam mining, which may be associated with higher exposure to silica. Further study is needed to characterise the responsible factors for the elevated CWP rates in central Appalachia.