A patient who died of rabies in Maryland recently had contracted the deadly viral infection through an organ transplant, health officials confirmed today.

The confirmation comes after tissue samples from the donor and recipient were tested by the CDC this week, according to a statement from the Centers for Disease Control and Prevention (CDC) and Maryland Department of Health and Mental Hygiene.

Three other patients who also received organs from the same donor have been identified and are now being evaluated and receiving rabies vaccination shots, the statement said. Those patients live in Florida, Georgia and Illinois.

The donor died after being admitted to a heathcare facility in Florida in 2011. At the time, rabies was not suspected as the cause of death, and the donor’s kidneys, heart and liver were sent to patients in need of organ transplants. The donor had moved to Florida from North Carolina shortly before becoming ill, and officials believe the donor was exposed to rabies in North Carolina, the statement said.

Rabies was only recently confirmed as the donor’s cause of death, after the current investigation began in Maryland. How the donor may have gotten rabies is still under investigation.

The rabies virus attacks the brain and nervous system. The rabies vaccine is typically given after a person has been exposed or possibly exposed to the rabies virus.

Both the recipient and the donor had the same type of rabies virus — a raccoon type, which can infect raccoons and other wild and domestic animals. Only one other person in the United States has ever been reported to have died from a raccoon-type rabies virus, the statement said. The most common way for people to get rabies in the U.S. is through contact with a bat, according to information from the CDC.

The CDC and health officials in all five states are now working to identify people who have had close contact with the donor or the four recipients and might need also need the vaccine.

The Maryland investigation began in early March, after the organ recipient there died. Officials found that the recipient had no reported animal exposures, and identified the possibility of transplant-related transmission of rabies, which is extremely rare.

The organ transplant occurred more than a year prior to the recipient’s death, which is a much longer time than the typical incubation period for rabies, of one to three months. There are other reports of cases of long incubation periods, the CDC said.

All potential organ donors in the United States are screened and tested to identify infection risks, the statement said. Questions are posed to family and close contacts, a physical exam is done, and tests are run for infectious diseases including HIV and hepatitis.

Typically, one to three cases of human rabies are diagnosed yearly in the United States.  If rabies is not suspected, testing for the virus is not routinely done on organ donors because it is difficult for doctors to confirm results in the short amount of time they have to keep the organs viable for a recipient.