CHICAGO - Four transplant patients have been infected with the AIDS virus in what a donor group says is the first such transmission in the United States in 13 years.

The transplants occurred in January at three Chicago hospitals. The patients infected with HIV and the virus for hepatitis C only learned of their status in the last two weeks.

Medical officials, citing privacy laws, say they are unable to release personal details about the donor.

However, they say tests on the donor for HIV, hepatitis and other conditions prior to the transplants all came back negative.

They say that means its is most likely the donor only acquired the infections in the three weeks prior to the donor's death.

Dr. Michael Millis, chief of the transplantation program at the University of Chicago Hospitals, says his staff was told of the problem Nov. 1, and brought in the two patients who had transplants there for testing the next morning.

"It was very surprising and devastating for them, I'll be honest, just as it would be for any of us," Millis said.

Based on the negative test results, doctors at Northwestern Memorial Hospital, Rush University Medical Center and the University of Chicago Medical Center went ahead with the transplants.

The right procedures were followed in testing the donor, said Alison Smith, vice-president for operations at Gift of Hope.

Joel Newman, a spokesman for the United Network for Organ Sharing, said the last known example of HIV being transmitted from a donor to a recipient was in 1994.

Millis said he thinks the process can be improved but may never be completely failproof.

"The organ supply is extraordinarily safe, but this has demonstrated that it's not 100 per cent safe and it is never going to be 100 per cent safe, at least with technology we have today," Millis said.