The U.S. Centers for Disease Control and Prevention is reporting a large, recent cluster of advanced black lung disease occurring among coal miners living and working in a single region of eastern Kentucky.
Between January 2015 and August 2016, 60 cases of progressive massive fibrosis (PMF) were identified among current and former coal miners at a single radiology practice, and the cases were later confirmed by investigators with the CDC's National Institute for Occupational Safety and Health (NIOSH).
Recent surveillance data indicate a resurgence of PMF among coal miners in the U.S. since 2000, but the 60 cases described in the report, published Thursday in the CDC's , were not discovered through routine surveillance.
NIOSH epidemiologist who led the investigation, told 鶹ý that cases of PMF fell sharply in the decades following passage of the Federal Coal Mine Health and Safety Act of 1969. PMF is essentially advanced black lung disease caused exclusively by dust exposure. "By the mid- to late 1990s it really wasn't being detected at all, but our surveillance has shown a very substantial resurgence [in subsequent years]," he said.
In the late 1990s the prevalence of PMF among miners participating in the Coal Act's voluntary surveillance program was less than 1%. By 2014 it had spiked to around 5%.
"It is clear that we still have too many miners being exposed to too much dust," Blackley said.
The newly reported PMF cluster involved miners residing in four contiguous counties in southeastern Kentucky (Floyd, Knott, Letcher, and Pike) that are part of the central Appalachia coalfield region.
The current and former miners had worked in coal mines for a mean of 29.2 years (range of 15 to 47 years), and their mean age at diagnosis was 60.3 (range of 44.9 to 77.4). All 60 patients had radiographic evidence of pneumoconiosis, and seven had large, rounded opacities on radiograph indicative of silicosis lung pathology.
"The factors or combination of factors that led to this increase in cases of PMF in eastern Kentucky and whether there are more unrecognized cases in neighboring coal mining regions are unknown," the investigators wrote.
They added that because PMF is associated with many years of dust exposure, it is not clear if specific exposures or mining practices contributed to the cluster of cases.
"New or modified mining practices in the region might be causing hazardous dust exposure. While obtaining detailed occupational histories, the reporting physician identified the practice of 'slope mining' as a potential exposure in eastern Kentucky," the researchers wrote.
This modified mining practice may be exposing miners in the region to high concentrations of respirable crystalline silica present in the quartz, which is the major component of sandstone, the team explained.
Twenty-six (43%) of the miners with PMF reported that their main job consisted of installing the bolts that support underground mine ceilings. The researchers noted that this job is associated with high silica dust exposure.
Twenty (33%) of the miners with PMF reported operating continuous miner machines for most of their careers.
"Operating a continuous miner machine has typically been considered a 'coal-face position' (i.e., a work position located at the face, or seam, of coal), and therefore not a position usually associated with higher silica dust exposures," the researchers wrote.
However, aspects of this job, specifically cutting rock above and below the coal seam, could lead to silica exposure, "which might explain why working as a continuous miner operator could pose an increased risk for PMF," they added.
"We are pretty confident that there were a number of miners who had mixed dust pneumoconiosis, with both coal and silica, but we can't be certain about the composition," Blackley told 鶹ý.
The identification of all 60 cases in a single radiology practice raises concerns that the actual prevalence of PMF in the area and surrounding coal mining regions may be much higher than has been recognized: "Finding these cases in such a small geographic area is a strong signal that action is needed in the area to identify existing cases at an earlier stage and prevent future cases."
Blackley noted that NIOSH is expanding its medical surveillance of coal miners. The Department of Labor's Mine Safety and Health Administration also recently changed standards to lower the level of allowable dust in mines and mandate the use of personal dust monitors by coal miners to measure real-time exposures.
Primary Source
CDC: Morbidity and Mortality Weekly Report
Blackley DJ, et al "Resurgence of progressive massive fibrosis in coal miners - Eastern Kentucky 2016" MMWR 2016; Dec. 15.