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Coal workers who died of black lung disease in recent years lost more years of life relative to their life expectancies than workers dying of the occupational disorder just a few decades ago, the CDC reports.

The study findings, published in , are consistent with a reported increase in a particularly aggressive type of black lung disease known as progressive massive fibrosis, or PMF.

In February of this year, the CDC's National Institute for Occupational Safety and Health (NIOSH) reported the largest cluster of PMF ever, with close to 600 cases identified at three medical clinics in southwestern Virginia between 2013 and early 2018. Clusters of the disease have also been identified in Kentucky and West Virginia coal regions.

Last May, the U.S. Department of Labor reported that 4,679 cases of PMF have been diagnosed among coal miners since 1970, with half of those cases occurring after 2000.

The resurgence of black lung disease among coal miners, starting in the mid-1990s, has been blamed, in part, on changes in mining practices. This includes longer shifts, increased surface mining and mining of narrower, lower-grade coal beds, which create more silica dust. Silica is much more toxic to the lungs than coal dust.

In the newly published analysis, NIOSH researchers identified black lung deaths among coal workers from 1999 to 2016, and calculated years of potential life lost to life expectancy overall (YPLL) and years of potential life lost before the age of 65 years (YPLL₆₅).

The overall number of coal workers dying of black lung disease, known medically as coal-workers' pneumoconiosis (CWP), decreased steadily from 1999 to 2016 -- a high of 409 workers in 1999 to a low of 112 in 2016.

But during this period, the mean years of potential life lost to life expectancy increased by 55.6%, from 8.1 years of life lost to 12.6 years per decedent. This increase was mostly observed in the years 2003 to 2016.

The researchers noted that the decline in the age-adjusted CWP death rate might be explained, in part, by the decline in employment in the mining industry.

The YPLL₆₅ per decedent ages 25 to 64 increased sharply at first -- from 4.3 in 2002 to 8.9 in 2005 -- before then gradually decreasing to 6.5 in 2016. Highest mean YYPLs₆₅ per decedent were 7.2 in 2000, 9.6 in 2004, and 9.3 in 2008.

"The growing gap between each decedent's actual age at death from CWP and his or her life expectancy corroborates recent reports of increasing prevalence and severity of CWP and of rapid disease progression among coal miners," the researchers wrote.

In CDC researchers reported an 8.6-fold increase in the prevalence of PMF from an annual average of 0.37% in the mid-to-late 1990s to 3.23% between 2008 and 2012 among miners in Kentucky, Virginia, and West Virginia participating in the Coal Workers' Health Surveillance Program.

"The sharp increase in YYPLs₆₅ was worrisome because it very likely reflected the increased prevalence we have observed in progressive massive fibrosis," NIOSH researcher Jacek Mazurek, MD, PhD, told 番茄社区app.

"We believe this finding is consistent with these earlier reports," he said. "Miners are dying earlier than would be expected and the gap is growing."

In 2014, the federal government decreased allowable exposures to respirable coal mine dust, made changes in dust monitoring, and directed NIOSH to expand medical monitoring for coal mine dust lung diseases.

CDC monitors miner health under the Coal Workers' Health Surveillance Program, established in 1969.

Mazurek said the reported PMF clusters and mortality data highlight the importance of continuing to closely monitoring miner health during their working years and in the years after they leave the mines.

It also underscores the importance of programs addressing primary exposure prevention, secondary prevention through early disease detection, and appropriate medical care of patients with coal workers' pneumoconiosis, the researchers concluded.

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