The Centers for Disease Control and Prevention says at least 23 people have been urged to get rabies shots following the disclosure that four patients received organs from an infected donor.

Public health agencies in Florida, Georgia, Illinois, Maryland and North Carolina began searching at least a week ago for people who may have been exposed.

A man in Maryland who got a kidney from the donor in 2011 died of rabies. Organs from the same Air Force airman went to three other recipients, all of whom remain healthy.

The CDC said Tuesday that health officials in the five states found more than 500 people who might have had contact with a recipient, the donor or an organ. About 90 percent of them have been assessed for risk of infection.