The recent outbreak of Legionnaires' disease at the Pittsburgh VA hospital in Oakland has caught the attention of U.S. Sen. Bob Casey.

Mr. Casey sent Veterans Affairs Secretary Eric K. Shinseki a letter Wednesday, looking for answers to the cause of what he termed a "preventable" problem that should not occur here or at VA hospitals around the country.

"It is my understanding that these cases could have been prevented had the VA been appropriately monitoring its water purification system," Mr. Casey, D-Pa., wrote in part in a letter to Mr. Shinseki. "It is a true disservice that veterans may come to the VA seeking help and potentially contract an additional medical condition, in a manner that is proven to be preventable."

Five people have been confirmed so far in the outbreak of the disease that spread through the water system at the Pittsburgh VA's University Drive Hospital. The VA said the first four have recovered, but the hospital has not said how the fifth patient is doing.

Pittsburgh VA spokesman David Cowgill did not return a call seeking comment.

A spokesman for Mr. Shinseki in Washington, D.C., said in an email, in part, that the VA would be providing a formal response to Mr. Casey.

The Pittsburgh VA, which treats about 270,000 veterans annually at its three area hospitals, first confirmed it had an outbreak and began treating the University Drive Hospital's water system Nov. 15.

Because Legionnaires' has an incubation period that can last 14 days, cases could still arise until at least today.

The senator's office said that after the cases were confirmed, it heard from several constituents concerned about the outbreak and from several people "on the ground" in Pittsburgh who said monitoring was an issue in the case.

Former Pittsburgh VA researchers Victor Yu and Janet Stout, both renowned Legionnaires' experts who left in 2006 and 2007, respectively, in a dispute with the Pittsburgh VA's management, told the Pittsburgh Post-Gazette last week that they believe the outbreak was the result of the poor management and maintenance of the water treatment system they installed at the hospital in 1993.

Mr. Casey's office said he was aware of the doctors' comments.

The treatment method, known as a copper-silver ionization system, releases minute amounts of the two metals that kill Legionella -- the bacterium that causes Legionnaires' disease -- in the water system.

The doctors and others said Pittsburgh VA knew it had a problem with the copper-silver system as far back as June. That was when it called in a consultant and showed the consultant prior periodic tests on the water system that found copper and silver readings that were both higher and lower than recommended levels.

But, an inside source said, the VA did not call anyone in to help adjust the levels until October, at about the time it was learning it may have an outbreak of Legionnaires' disease.