ATLANTA — Calling it a “miraculous day,” an American doctor infected with Ebola left his isolation unit and warmly hugged his doctors and nurses on Thursday, showing the world that he poses no public health threat one month after getting sick with the virus.

Dr. Kent Brantly and his fellow medical missionary, Nancy Writebol, who was quietly discharged two days earlier, are still weak but should recover completely, and no one need fear being in contact with them, said Dr. Bruce Ribner, who runs the infectious disease unit at Emory University Hospital.

Brantly’s reappearance was festive and celebratory, a stark contrast to his arrival in an ambulance under police escort three weeks earlier, when he shuffled into the hospital wearing a bulky white hazardous materials suit.