A Maryland man who two weeks ago became the state’s first fatal case of rabies in nearly 40 years contracted the infection from a kidney transplant, according to two people familiar with the case.

Three other people--in Georgia, North Carolina and Illinois--received organs from the same donor. They have been located and have started rabies-prevention treatment.

“They’re doing fine,” Matthew Kuehnert, a physician at the Centers for Disease Control and Prevention, said Friday morning, confirming the case reported earlier by The Washington Post. The CDC is assisting county, state, military and other federal agencies investigating the case.

It is only the third time on record rabies has been transmitted by transplantation of c“solid” organs such as kidneys and livers. A cluster of cases occurred in Texas in 2004 and in Germany in 2005.

The recipient died at the Veterans Affairs Medical Center in Washington after being in the hospital for about a month, according to the people with knowledge of the case, who spoke on the condition of anonymity. He had received a kidney from a Florida man in an operation at the Walter Reed National Military Medical Center in 2011.

CDC laboratory scientists earlier this week determined that the rabies virus obtained from the recipient was genetically identical to the virus recovered from the organ’s donor.

Untreated rabies is almost always fatal. People vaccinated after becoming infected but before symptoms develop usually survive. Richard Franka, director of the CDC’s rabies lab, said that “maybe dozens” of people who had contact with either the donor or recipient will need to get rabies vaccination--a course of four shots. Some have already started.

Transmission of rabies through organ or tissue transplant is extremely rare. Four people in Texas died in 2004 from rabies contracted from a single donor’s tissue. There have been at least eight cases around the world contracted through cornea transplants.

Investigation of the case involves county, state, federal and military epidemiologists, physicians and laboratory scientists.

Rabies was suspected shortly before the recipient’s death but was not confirmed until his brain was examined in an autopsy. The idea that he could have contracted the infection from the transplanted kidney was initially doubted because of the extremely long time — about 15 months — between the surgery and his death. The incubation of rabies cases is rarely longer than three months.

In general, fewer than five cases of rabies are diagnosed each year in the United States. Most often the virus is acquired by contact with a bat. Bites from infected raccoons and dogs, or contact with their saliva, account for most of the rest. How the Florida man may have contracted the infection could not be learned.

The virus travels up nerves to the brain, a process that takes weeks or months if the entry wound is far from the head (as in the foot). Symptoms are varied and occasionally dramatic, such as the fear of swallowing water known as hydrophobia. The patient usually slips into a coma and dies of respiratory failure.

The donor, described as a man in his 20s, died of encephalitis, a general term for inflammation of the brain. The condition has many causes. Viruses such as herpes simplex and West Nile virus are among the more common. Rabies is among the rarest.

Details of the donor’s medical care could not be learned. In particular, it was not known what tests were done and which diagnoses were considered before he died. But rabies was not diagnosed until his brain, which had been preserved, was examined after the death of the recipient in Washington.

Potential organ donors are screened for a standard battery of infectious diseases before their organs are offered. Rabies is not one of them, however.

“The decision whether to accept or reject an organ is an independent medical judgment based on the testing and information the physicians have on the potential donor,” said Joel Newman, a spokesman for the United Network for Organ Sharing, the national organization in Richmond that helps coordinate transplants.

What screening tests were done on the donor and his tissue in addition to the usual ones also could not be learned. Blood tests usually reveal antibodies to the virus, and the infection is confirmed by examining thin slices of brain tissue under a microscope. Several experts said it is unlikely that rabies could be ruled out for certain within the time window in which a transplant has to be done.

“Everyone was taken aback that someone who dies of encephalitis is considered acceptable to donate an organ,” said one person involved in the case.

Organs from people with known infections are, however, occasionally transplanted. In some cases, the recipient already has the infection, such as hepatitis C. In other cases, the patient and physicians conclude that the risk of dying from the infection is less than the risk of dying while waiting for another organ.

“You balance the probability of infectious complications with the cost of not undergoing the transplant,” said Dorry Segev, a transplant surgeon and epidemiologist at Johns Hopkins University who had no involvement in the case. “The risk of death on dialysis is anywhere between 5 to 15 percent per year, and sometimes higher.”

Segev said that transplanting an organ from someone who died of an infection whose cause was not known would be “incredibly rare” but that it occasionally happens.