Federal researchers are seeing an increase in the amount and severity of black lung disease among coal miners in far Southwest Virginia.

The U.S. Centers for Disease Control and Prevention released those findings last month in its national publication, the Morbidity and Mortality Weekly Report.

The report describes 11 newly identified cases of advanced black lung disease -- medically known as coal workers' pneumoconiosis -- in coal miners in Lee and Wise counties. Researchers are analyzing similar data from Dickenson, Russell, Tazewell and Buchanan counties.

The report confirmed that the number of cases of black lung disease is rising in Lee and Wise counties and that the cases are more severe, said Vinicius Antao, medical officer of the division of respiratory disease studies for the National Institute for Occupational Safety and Health and the lead researcher on the project.

But researchers aren't sure why.

Black lung disease is caused by the inhalation of coal dust. In 1969, a federal law was passed that mandated dust limits to protect miners' health and the number of miners who developed the disease decreased, according to the study.

Then in 2003, a study that tracked miners in different parts of the United States from 1996 to 2002 identified clusters of rapidly progressive cases of black lung disease in certain parts of the United States, particularly in eastern Kentucky and Western Virginia.

The recent report on the coal miners in Lee and Wise counties built on the previous findings. Researchers stated in the report that the results of the increase in the number of cases and in their severity "should be considered a sentinel health event and justifies a comprehensive assessment of current dust-control measures."

"Something doesn't add up, because we're seeing lots more disease than would be expected at those levels of dust," Antao said.

In the recent CDC report, researchers examined 328, or 31 percent, of the estimated 1,055 underground coal miners who were employed in March and May 2006 in Lee and Wise counties. They ranged in age from 21 to 63 and had worked in the mines for an average of 23 years.

Thirty of the miners whom researchers examined had evidence of black lung, and of those, 11 had advanced cases, according to the report.

The average age of the miners with the advanced cases was 51, and they had spent an average of 31 years working in underground coal mines.

Researchers suggested several possible reasons for the increase in the number and severity of the black lung cases: that the current allowable dust limit may be too high; that the levels of coal dust reported might be underestimated; and that the toxicity of the coal being mined may be higher -- although the report acknowledged the types of coal in the Lee and Wise counties have not been associated with higher toxicity.

Dr. Randy Forehand is a specialist in respiratory medicine at Lewis-Gale Medical Center in Salem who has treated patients with black lung disease in Richlands for 16 years. He said the theory used to be that if coal dust was controlled, black lung disease would go away.

"Overall, the levels [of coal dust] and incidences [of black lung disease] are going down, except in these hot spots," Forehand said.

National Institute for Occupational Safety and Health investigators have suggested that they are seeing more cases of miners with black lung disease in small, nonunion mines.

The study that tracked 1,749 coal miners in Virginia from 1996 to 2002 found that 8.6 percent of them had coal miners' pneumoconiosis and 0.6 percent had an advanced form of the disease, known as progressive massive fibrosis.

Genetics also plays a role in who develops black lung disease, Forehand said.

"Not everybody who works down there gets it," he said.