It remains the first and only cluster of PV ever recorded in the United States, though the condition only became reportable to state cancer registries in 2001 and officials said it's statistically likely there are others.
Residents in the affected ZIP codes were four times as likely to suffer from PV as residents living in outlying areas, according to the government.
Researchers cautioned, though, that their investigation was not designed to uncover an environmental link to PV, a cancer that results in the overproduction of red blood cells and can lead to heart attack or stroke. PV's cause is unknown.
"We don't want to give the message that there are no connections," said ATSDR researcher Vince Seaman. "We just don't have the data."
Some residents blame their illnesses on a recycler called McAdoo Associates that accepted hundreds of thousands of gallons of paint sludge, waste oils, used solvents, PCBs, cyanide, pesticides and many other known or suspected carcinogens.
Environmental officials shut down the site in 1979, and it was later placed on the federal Superfund list and cleaned up. Other Superfund sites dot the area, too, along with a power plant that burns waste coal that some residents also suspect has caused health problems.
Researchers said they confirmed 33 cases of PV in Luzerne, Carbon and Schuylkill counties. That was a slightly lower number than they reported last October, at the conclusion of their preliminary investigation into the cluster.
ATSDR revealed its latest findings at a community meeting in Hazleton on Monday night.
Researchers said they found that Pennsylvania does not accurately report the number of PV cases statewide. That's because the criteria for diagnosing the illness has changed, and because PV is only reported by hospitals. (Not all PV patients are hospitalized.)
Seaman said inaccurate PV reporting is likely a problem in other states.
Also Monday, U.S. Sen. Arlen Specter announced that the Senate Appropriations Committee has approved $262,000 for a planned Drexel University investigation into the cluster. The funding has yet to clear the full Senate.
"It is clear that more research is necessary to pinpoint the reasons for this cluster, including whether environmental contaminants are a factor," Specter said a statement.
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