By Julie Steenhuysen

CHICAGO, Nov 13 (Reuters) - Four transplant recipients at three Chicago hospitals have contracted HIV and hepatitis C from a single organ donor, U.S. health officials said on Tuesday.

The cases mark the first incidence of HIV infection contracted from organ donation in more than 20 years, according to Dr. Matthew Kuehnert, who oversees organ safety at the U.S. Centers for Disease Control and Prevention.

Kuehnert said outside testing has confirmed that both the donor and all four transplant recipients have tested positive for both HIV and hepatitis C.

"It is very unlikely that all four would be infected with HIV and hepatitis C by chance," Kuehnert said in a telephone interview.

He said the CDC is conducting its own tests to match the strain of HIV in the donor with the infected recipients and to determine the best course of treatment.

Hospital officials confirmed that two patients at the University of Chicago Medical Center, one patient at Northwestern Memorial Hospital and one at Rush University Medical Center tested positive for HIV or human immunodeficiency virus, which causes AIDS.

"All of the policies were followed correctly and all of the tests were done correctly. Unfortunately, the tests came back as a false negative result," said Mandy Claggett, a spokeswoman for United Network for Organ Sharing or UNOS, which sets policy for organ donation and has been monitoring the investigation.

'ALWAYS RISK'

Kuehnert said the organs came from a high-risk donor, meaning from someone who fit under one of several criteria that would increase the chances that the person might have be infected with HIV.

Those include men who have had sex with another man in the preceding five years, intravenous drug users, prisoners, and people who have had sex for money or drugs.

Dave Bosch of the Gift of Hope Organ and Tissue Donation, the regional organ procurement agency that handled the donor organs, said the donor's high-risk status was confirmed on a questionnaire. "We were aware of that from the beginning," he said.

But standard testing using the enzyme-linked immunosorbent assay or ELISA antibody screening test was negative.

When Gift of Hope was notified of the infections, it sent samples from the donor to an outside lab, Bosch said. A second ELISA test turned up negative, but a more sensitive test called the nucleic acid-amplification test or NAT was positive.

Bosch said it is possible the HIV infection in the donor occurred within three weeks of donation -- too recent for the ELISA test to detect.

He said Gift of Hope and others involved in organ donation are weighing which test might be best against the need for the need for rapid testing.

He said about 9 percent of the 22,000 organ transplants in the United States involve high-risk organs.

The CDC's Kuehnert said the problem is part of the risk that goes with organ transplantation.

"You can't disinfect an organ. You can't process it. There is always going to be some risk," Kuehnert said.

"One thing people should take from this is that the reason there are high-risk donors being accepted is because of a lack of available organs," he said.

"For someone on the organ transplant list, they should talk to their physician about the risk," he said.

(Editing by Eric Walsh)

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