Federal health researchers have tested nearly 2,200 people in northeastern Pennsylvania for a genetic mutation associated with a rare blood cancer.

The testing found the mutation in 19 people, or 1.6 percent of those who participated in the study. Scientists don't yet know how prevalent this mutation is in the general population.

The testing was performed after government epidemiologists confirmed a cluster of polycythemia vera, or PV, a cancer that results in the overproduction of red blood cells and can lead to heart attack or stroke.

Three Superfund sites, a power plant and several abandoned strip mines are among the culprits suspected of making people sick in a 20-mile stretch between Hazleton and Tamaqua.

The cause of PV is unknown.