ATLANTA — A medical plane transporting the fourth American aid worker sickened with the Ebola virus landed in metro Atlanta this morning, with the patient headed to Emory University Hospital, where two others have been successfully treated.

The plane touched down about 9:20 a.m. at Dobbins Air Reserve Base in Marietta, just northwest of Atlanta. Air Force spokesman Lt. Col. James Wilson confirmed the arrival.

The patient will be housed in a special isolation unit, hospital officials said. The patient’s identity was not released, and the hospital released no additional details.

But the World Health Organization says a doctor who has been working in an Ebola treatment center in Sierra Leone has tested positive for the disease. It said the doctor was in stable condition Monday in Freetown and was being evacuated.

Last month, two U.S. aid workers who contracted Ebola in Liberia, Dr. Kent Brantly and Nancy Writebol, were treated successfully at Emory.

Another worker, Dr. Rick Sacra, 51, is being treated at the Nebraska Medical Center in Omaha. In Omaha, Sacra’s family members said he was able to eat breakfast Monday for the first time since arriving Friday at the Nebraska hospital.

The doctor from Worcester, Mass., remains in stable condition.

He went to Omaha instead of Atlanta because federal officials asked the medical center to treat him to prepare other isolation units to take more Ebola patients if needed.

The Ebola outbreak sweeping West Africa has killed more than 2,000 people and has taken a particularly high toll on health care workers.