Three veterans treated at the St. Louis VA Medical Center's dental clinic have tested positive for hepatitis and further testing will be necessary to determine if inadequately sterilized dental equipment is to blame, VA officials said Friday.

The Department of Veterans Affairs provided test results to The Associated Press after repeated requests over the past two weeks. The VA has drawn criticism from some members of congressional delegations in Missouri and Illinois for taking too long to release information on how many veterans tested positive.

The results come about a month after the VA sent letters to 1,812 veterans treated at the clinic from Feb. 1, 2009, through March 11, 2010, urging them to take blood tests because improperly cleaned dental equipment could have exposed them to hepatitis B, hepatitis C or HIV. The VA has said the risk of infection is remote.

A fourth veteran also tested positive, but the VA said later Friday that the infection happened before Feb. 1, 2009.

Of 1,022 veterans tested and notified of results, two tested positive for hepatitis B and two for hepatitis C, the VA said. None have tested positive for HIV, the virus that causes AIDS. The VA did not provide more details.

The VA said extensive epidemiological testing is under way to try and determine how long each of the three veterans has been infected and the source of the infections. It wasn't clear how long that process would take.

The VA said 1,598 veterans have responded to the disclosure letter or called to set up an appointment for testing. Thirteen have declined to be tested.

The U.S. Centers for Disease Control and Prevention website says hepatitis refers to a group of viral infections that affect the liver. Viral hepatitis is the leading cause of liver cancer and the most common reason for liver transplants. The CDC said an estimated 1.2 million Americans are living with chronic hepatitis B and 3.2 million are living with chronic hepatitis C.

The CDC said many who have hepatitis don't know it.

Two Missouri congressmen, Democrat Russ Carnahan of St. Louis and Republican Roy Blunt of Springfield, said they were saddened to learn that four veterans were ill. Carnahan said he still had concerns about how the VA is handling test results.

"If there were any individuals who tested positive, even if that test was preliminary, the VA should not have kept them in the dark," Carnahan said. "They should have been notified immediately so they could take precautions to protect their spouses and loved ones."

Blunt said, "The VA has a lot of work to do to regain our veterans' trust, and I still await a response as to how the VA plans to make this situation better."

A VA spokeswoman declined comment on Carnahan's concerns about why it took so long to release test results. In a Web notice, the VA offered some explanation, saying its initial testing is thorough, and some veterans chose to be tested at clinics other than those operated by the VA, slowing test results.

The VA began an internal investigation into what went wrong at St. Louis soon after the problem was disclosed. But members of Missouri and Illinois congressional delegations have expressed a preference for an independent investigation.

On Thursday, two were announced. The inspector general for the Department of Veterans Affairs agreed to look into the mistakes. Also, the Government Accountability Office — the investigative arm of Congress — widened its ongoing investigation into other VA medical center mistakes to include the situation in St. Louis.

Last year, the VA said 10,000 veterans treated at its hospitals in Miami, Murfreesboro, Tenn., and Augusta, Ga., were potentially exposed to HIV and hepatitis, also because of faulty sterilization, in this case of equipment used for colonoscopies and other procedures.