Two American aid workers discharged from hospital after being treated for the deadly Ebola virus pose no public health risk, their hospital carers said.

Officials in Atlanta announced the release of Dr Kent Brantly and Nancy Writebol today.

Dr Brantly left Emory University Hospital today and Dr Writebol left on Tuesday. Family and officials say they're free of the virus.

Dr Writebol's husband says she left privately in a weakened condition to recuperate at an undisclosed location.

They were at the hospital nearly three weeks after being infected with the virus in Africa.

Dr Bruce Ribner, medical director of the infectious disease unit at the hospital, said at a news conference that their release did not pose a public health risk.

At the news conference, Dr Brantly said it is "a miraculous day".

Dr Brantly, 33, said: "I am thrilled to be alive, to be well, and to be reunited with my family. As a medical missionary I never imagined myself in this position.

Dr Brantly and his wife stood holding hands before he read from a written statement. He choked up several times while thanking his aid group, North Carolina-based Samaritan's Purse, and the Emory medical team standing behind them.

After speaking, the couple hugged the medical staff and joked with them. Several blinked back tears, then cheered and applauded as Dr Brantly and his wife made their way from the room.

In his statement, David Writebol said Nancy, 59, "was greatly encouraged knowing that there were so many people around the world lifting prayers to God for her return to health. Her departure from the hospital, free of the disease, is powerful testimony to God's sustaining grace in time of need."

Dr Brantly was flown out of the west African nation of Liberia on August 2, and Dr Writebol, followed on August 5. The two were infected while working at a missionary clinic outside Liberia's capital.

They received an experimental treatment called Zmapp, but it's not known whether the drug helped or whether they improved on their own, as has happened to others who have survived the disease. The treatment is so novel that it hasn't been tested in people.

The limited supply of Zmapp also was tried in a Spanish missionary priest, who died, and three Liberian health care workers, who are said to be improving.

The Ebola outbreak has killed more than 1,300 people across West Africa. There is no proven treatment or vaccine. Patients are given basic supportive care to keep them hydrated, maintain their blood pressure and treat any complicating infections. Ebola is spread only through direct contact with the bodily fluids of sick people experiencing symptoms.