A Maryland patient who died of rabies did not get the disease from an animal, but rather an organ transplant done more than a year earlier, the Centers for Disease Control and Prevention announced Friday morning.
Rabies is a rare infection in the United States, accounting for one to three human cases per year. The Maryland Department of Health and Mental Hygiene began investigating the case after the patient died this month and investigators identified the possibility of transplant-related transmission of rabies -- "which is extremely rare," the CDC said in a statement.
The CDC confirmed to CBSNews.com that the patient had underwent a kidney transplant.
The patient was one of four people who had received organs from the same donor, who became ill in 2011 and died at a Florida health care facility. The donor's organs, including the kidneys, heart, and liver, were sent to recipients in Florida, Georgia, Illinois and Maryland.
The CDC tested tissue samples from the donor and the deceased recipient to confirm rabies transmission was caused by organ transplantation.
How could this have happened?
All potential organ donors in the U.S. are screened and tested to see if they have an infection that could possibly spread through transplantation. Typically doctors will test for HIV or hepatitis, and conduct interviews with family members and close contacts to determine donor eligibility. Rabies had not been suspected as the cause of death, according to health officials.
"If rabies is not clinically suspected, laboratory testing for rabies is not routinely performed, as it is difficult for doctors to confirm results in the short window of time they have to keep the organs viable for the recipient," the CDC said.
The other three organ recipients have been identified by health officials, and are receiving rabies vaccines.
"Organ screening is designed to ensure safe and successful transplantations," according to the CDC. "The benefits from transplanted organs generally outweigh the risk for transmission of infectious diseases from screened donors."
The form of rabies that killed the organ donor and recipient is especially rare in humans, according to the CDC. It's called "rabies virus-a raccoon type," which can infect raccoons and other wild and domestic animals. Only one other person is reported to have died from this type of rabies, the CDC reported.
The Fla. donor had lived in North Carolina, where the rabies exposure may have occurred. The CDC is working with officials in all five affected states (Fla., Ga., Ill., Md., and N.C.) to identify people who came in close contact with the organ donor or four recipients.
Each year, an estimated 40,000 Americans receive a rabies vaccines due to potential exposure to the disease. Generally, pets are more likely to come in contact with rabid animals than humans, so the CDC urges people to take their pet to a veterinarian on a regular basis and stay up-to-date with all rabies shots.
Untreated, rabies can cause flu-like symptoms at first such as weakness, fever or headache. As the disease progresses over the course of a month, an infected person may experience anxiety, confusion, abnormal behavior, hallucinations and insomnia.
Typically, rabies has an incubation period of one to three months, but these new cases are consistent with some other reports of longer incubation periods.
The CDC has more information on rabies.