The donor of a kidney that transmitted a fatal case of rabies to a Maryland man was a 20-year-old airman in Pensacola, Fla., training to be an aviation mechanic. When he fell ill two summers ago, physicians thought he had food poisoning from eating fish from the Gulf of Mexico.

His death in a coma three weeks later was attributed to an intestinal infection, dehydration and seizures. He actually died of rabies. The viral infection wasn’t suspected before he died, and his organs were offered for donation. It apparently also wasn’t suspected when his brain was examined in an autopsy.

Tests this week revealed the virus was a type found in raccoons in North Carolina and Virginia. The man was from North Carolina but hadn’t returned home after enlisting in the Air Force 17 weeks before his death. That suggests the virus had been incubating for months before it made him ill.

Those are among the facts epidemiologists are stitching together as they reconstruct a tragic sequence of events that ended in late February with Maryland’s first fatal case of rabies in 36 years.

“We are questioning the donor’s family and friends. We know that he was an avid hunter and fisherman. He might have come into contact with wildlife somehow. We don’t know more at this time,” Richard Franka, head of the rabies laboratory at the Centers for Disease Control and Prevention, said Friday.

Whether it’s too risky to use organs from people who die in a coma of unknown causes has been debated by the U.S. transplant community for several years. A 2011 study showed that over a recent three-year period, seven people had developed brain infections, three of them fatal, from donated organs.

In June 2012, the United Network for Organ Sharing (UNOS) warned transplant teams that “extreme caution is urged” before using organs from people with encephalitis — brain inflammation — that might be caused by untreatable viruses such as rabies and West Nile. It did not issue a blanket prohibition.

“The devil is in the details,” said Michael D. Green, an infectious diseases physician at the University of Pittsburgh who heads UNOS’s Disease Transmission Advisory Committee. “But clearly one needs to be exceptionally cautious.”

There are differing reports whether the airman’s physicians thought he had encephalitis.

The man spent four days at the air station’s hospital in late August 2011 after suffering abdominal pain and vomiting, according to Cynthia Smith, a Department of Defense spokeswoman. As he became more ill, he was transferred to a civilian hospital in Pensacola, which hasn’t been identified. There he became confused, developed respiratory problems and lapsed into unconsciousness. He was declared brain dead on Sept. 7, 2011.

Other people involved in the investigation say the airman’s physicians initially thought he had ciguatera, a food-borne illness caused by toxins that accumulate in the flesh of saltwater fish feeding on certain reef microorganisms. By the time of his death, however, that had been ruled out.

Smith said the cause of death was “acute severe gastroenteritis, complicated by dehydration, electrolyte abnormalities, and seizure.” However, Matthew Kuehnert, a physician who heads CDC’s office of tissue safety and is helping investigate the case, said the Florida physicians thought the man had died of a brain disease.

“They thought it was an encephalitis of unknown etiology [cause],” Kuehnert said.

Was rabies considered?

“Not to our knowledge,” Kuehnert said. “The patient was not tested for rabies either during clinical care or after death at autopsy.” He added that it “is not unusual for rabies not to be thought of in a patient with encephalitis. It is a very rare disease.”

A microscopic examination of brain tissue might have revealed changes characteristic of rabies. By then, however, one kidney had been transplanted into a 48-year-old Army veteran in an operation at Walter Reed Military Medical Center. Three other organs — another kidney, the liver and the heart — were transplanted into patients in Georgia, North Carolina and Illinois.

Kuehnert said Friday all of them have been found and have started treatment, which consists of an injection of rabies-fighting antibodies and four vaccination shots over a month.

“They’re doing fine,” he said.

People exposed to the two men are also being tracked down. “Maybe dozens” will need to be vaccinated too, Franka said.

Rabies was not initially suspected in the Maryland man, either.

He’d gone to the Veterans Affairs hospital in Washington with stomach complaints and then developed weakness and confusion. He died after three weeks on a ventilator. His blood tested positive for rabies antibodies, but other tests were negative. Testing of the brain tissue proved for certain he had the infection.

Even once rabies was suspected, the man’s physicians doubted he could have gotten it from the kidney he’d received 15 months earlier, investigators said. That’s because rabies symptoms rarely appear more than three months after a person is infected (usually by an animal bite).

The airman’s case appears to have had a long incubation period too — at least four months. Kuehnert said such long incubation could be a property of the subtype of virus the men had.

A spokesman for UNOS, Joel Newman, said there are 74,851 “active candidates” for organ transplant in the United States. About 58,000 need kidneys. Most will be on the list for at least four years before they get an organ. Last year, 5,996 people died awaiting organs, most of them awaiting kidneys.