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Is the increasing prevalence and severity of coal workers' pneumoconiosis in the United States due to increasing silica exposure?
  1. Robert A C Cohen
  1. Correspondence to Robert A C Cohen, Division of Pulmonary and Critical Care Medicine, Stroger Hospital of Cook County, 1900 West Polk Street, Suite #1402 Chicago, IL 60612, USA; bobcohen{at}

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In this issue of Occupational and Environmental Medicine, Laney et al (see page 652) describe a recent increase among United States coal miners in the prevalence of chest radiographic patterns classically associated with silicosis.1 The authors analysed data from the US Coal Workers' X-ray Surveillance Program (CWXSP) in an attempt to investigate the cause(s) of the increasing prevalence of radiographic coal workers' pneumoconiosis (CWP) in the USA, and the recent reports of rapidly progressive forms of CWP and advanced stage CWP in younger miners.

In 1969, the United States Congress passed the Coal Mine Health and Safety Act which mandated a permissible exposure limit of 2 mg/m3 for respirable coal mine dust in US coal mines. The exposure limit is further reduced when the concentration of crystalline silica in the mine atmosphere exceeds 5%.2 Following adoption of these public health measures, the prevalence of CWP among miners examined through the CWXSP declined from approximately 30% in the early 1970s to 2% for the period of 1995–1999.3 However, since 2000, the tenure-standardised prevalence of simple pneumoconiosis and progressive massive fibrosis (PMF) has increased.4 Recently, rapidly progressive pneumoconiosis and advanced pneumoconiosis have been reported in relatively young miners.5–7 These findings were not uniform across the …

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