The plight of two kidney transplant patients who contracted a brain infection from an organ donor is prompting health officials to re-examine their policies on using people with certain neurological conditions as donors.

The organ donor, a child at the University of Mississippi Medical Center in Jackson, had had seizures and a brain disorder initially thought to be an autoimmune disease and not transmissible. The real cause of his illness turned out to be a rare, usually fatal infection, but the mistake in diagnosis was not recognized until the transplants were done and the two recipients had become critically ill. The medical center disclosed the situation on Dec. 18.

The case highlights the lack of a national policy on whether to bar people with poorly defined neurological disorders as donors. For now, the decision is up to individual transplant centers, said Dr. Michael G. Ison, chairman of an advisory committee on infectious disease transmission for the United Network for Organ Sharing, which coordinates transplants in the United States.

While Dr. Ison declined to comment on the Mississippi case, he said, ''The bigger issue is that in cases in which a patient has a neurologic condition that hasn't been definitively diagnosed, that is associated with altered mental status, most experts would recommend against the use of organs from those donors.''

Dr. Ison, an assistant professor at Northwestern University and a specialist in infectious diseases, said the Mississippi case spurred his committee to begin looking at nationwide data to see how often such patients become donors.

Dr. Shirley Schlessinger, the medical director for the Mississippi Organ Recovery Agency and a transplant nephrologist at the university medical center, said that the university had done extra tests to see if the organs were safe to transplant.

''This will be discussed by a collaborative group of experts at a national level'' to try to make the system safer, Dr. Schlessinger said. But she added: ''I think it's wrong to say we're going to eliminate all these people we can't be sure of. There will always be undetectable disease in the setting of solid organ donation. We have to stratify the risk and present it to recipients.''

Disease transmission from transplants occurs in 1 percent of cases involving deceased donors, according to data the organ network began collecting in 2005. But reports are increasing as centers become aware of the network's database. Recipients have contracted West Nile virus, rabies, H.I.V., tuberculosis, a rodent virus, parasitic worms and other infections. In a few cases, donors have even transmitted cancers.

Transplant patients are especially vulnerable because the drugs needed to prevent organ rejection work by suppressing the immune system.

In October, a government report focused on the need for ''biovigilance'' in preventing infections from donors.

Dr. Eileen Farnon, an epidemiologist at the Centers for Disease Control and Prevention, said, ''This is a difficult topic, because organs are really scarce and patients who need a transplant are typically quite ill and need a transplant quickly, and sometimes it's hard to do all the testing that one could possibly think of for all the infections out there.''

More than 100,000 people are on a waiting list for a transplant, and 9,000 die each year, the organ network says.

Experts at the disease centers are investigating the case and advising in the patients' treatment.

Dr. Matthew J. Kuehnert, the director of the office of blood, organ and other tissue safety at the disease centers, said that transplant patients are sometimes an early warning system for new infectious diseases. He said the nation needed a ''sentinel network'' to collect information about donors and transplant patients and notify doctors when an organ or tissue recipient gets sick.

''That would both potentially help clinicians taking care of patients already transplanted,'' Dr. Kuehnert said, ''but also in the case of tissues, which sometimes take longer to be transplanted, because they can be stored, it would help clinicians before they transplanted them into a donor.''

He added, ''I think organ safety has not been a priority in transplantation.''

Dr. Richard B. Freeman, who performs liver and kidney transplants at Tufts Medical Center, disagreed. Dr. Freeman said too much effort was being spent worrying about a small number of infections, while far more patients were being harmed by a lack of donors. He said that transplant centers should do a better job of recognizing risky situations and informing patients, so that they can decide whether to accept particular organs.

The organ donor in Mississippi was a boy who died in November at the university medical center. He was being treated for seizures. Doctors did not realize it at the time, but he had a brain infection caused by a type of amoeba. The infection is rare, and exceedingly difficult to detect.

The mistaken first diagnosis was acute disseminated encephalomyelitis, an inflammation of the brain and spinal cord that is thought to be caused by the patient's own immune system. That condition is not contagious, but the diagnosis is not really definitive; it is made when everything else has been ruled out.

Given that there was an element of uncertainty, doctors tested the boy for many more infections than organ donors are routinely screened for, Dr. Schlessinger said. All the tests were negative, so his heart, liver and kidneys were transplanted into four patients. Afterward, an autopsy still missed the infection and seemed to support the mistaken diagnosis.

About three weeks after the transplants, both kidney recipients became severely ill, within hours of each other, with seizures, fever and changes in their mental status. They were taken back to the hospital in Jackson. A doctor there noted that both had had kidney transplants the same day. He suspected immediately that the kidneys had come from the same donor and that the donor might have had an undetected infection.

The hospital sent samples of the donor's brain tissue to the disease centers, which found an amoeba called Balamuthia mandrillaris. One kidney patient was then given a biopsy, which also tested positive for the amoebas. Balamuthia lives in soil and water, and scientists suspect that people become infected through cuts or from ingesting the organism. Only about 70 cases have ever been identified in the United States, and nearly all have been fatal. These are the first known cases from transplants.

It was not clear why only the kidney patients had become ill. The kidneys may have harbored more amoebas than the other organs, Dr. Farnon said, or the particular anti-rejection drugs might have been a factor.

The patients are being treated with ''a boatload of drugs,'' Dr. Schlessinger said, but have not improved.


''It would be difficult to say, 'Don't ever recover a donor with encephalitis,' '' he said. ''Some may be O.K. But we don't know how many times it's a successful operation, and how many times a tragic operation.''

PHOTO: A kidney transplant at Georgetown University Hospital. For now, individual transplant centers make decisions on donors. (PHOTOGRAPH BY MANUEL BALCE CENETA/ASSOCIATED PRESS)