MONDAY, Sept. 29, 2014 (HealthDay News) -- Another American doctor exposed to the Ebola virus while working in West Africa was admitted Sunday to a hospital at the National Institutes of Health in suburban Washington, D.C.

The unidentified patient was working at an Ebola treatment unit in Sierra Leone when exposed to the highly lethal virus that has been ravaging four West African nations for months.

The patient was admitted to the NIH Clinical Center's special clinical studies unit "out of an abundance of caution," the agency said in a news release. The unit's staff is "trained in strict infection control practices optimized to prevent spread of potentially transmissible agents such as Ebola," the release said.

Dr. Anthony Fauci, director of the NIH's National Institute of Allergy and Infectious Diseases, wouldn't discuss details about the patient. But he told the Associated Press that exposure to the Ebola virus doesn't automatically mean someone will become sick.

"When someone is exposed, you want to put them into the best possible situation so if something happens you can take care of them," Fauci said.

The patient poses minimal risk to the NIH staffers and the public, the news release said.

The patient is the fifth U.S. health care professional exposed to the Ebola virus while working in West Africa.

Three others who became infected with the virus have recovered, while a fourth continues to undergo treatment at Emory University Hospital in Atlanta.

The third American Ebola patient to become infected -- a medical missionary -- left a Nebraska hospital on Thursday, free of the virus.

Treatments given to Dr. Rick Sacra, 51, included doses of an experimental drug and blood transfusions from a fellow U.S. medical missionary who also survived infection with the virus.

"The CDC [U.S. Centers for Disease Control and Prevention] has declared me safe and free of virus," Sacra said during a Thursday morning news conference at Nebraska Medical Center in Omaha. "Thank God. I love you all."

Sacra said his friend and fellow medical missionary and Ebola survivor, Dr. Kent Brantly, "communicated with me about a week ago and let me know in no uncertain terms that this was not going to be a quick recovery. So I have to take things one day at a time." Brantly gave blood to Sacra in the hope that antibodies to the Ebola virus would aid Sacra in his recovery.