ATLANTA (AP) — 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.

"I am thrilled to be alive, to be well, and to be reunited with my family," Brantly said, choking up as he read a written statement. Then he and his wife turned and hugged a parade of doctors and nurses, hugging or shaking hands with each one. For some, it was their first direct contact without protective gear.

After Brantly, 33, and Writebol, 59, were infected while working with Ebola victims in Liberia, their charity organizations, Samaritan's Purse and SIM, reached out to top infectious disease experts for help.

Working connections, they obtained one of only five courses available worldwide of an experimental drug known as Zmapp, and Brantly and Writebol split the doses before being evacuated to Atlanta. The other four were later given to a Spanish priest, who died, and three doctors in Africa, who have been improving.

Brantly didn't take questions at Thursday's news conference, but he did briefly describe how they confronted Ebola back in Liberia. He said aid workers had begun "preparing for the worst" after learning of the outbreak in March, and saw their first patient in June. Soon, many more arrived.

He said his team took all the precautions they could. After his wife and children returned to the U.S. for a family wedding, he focused on work, moving patients to a bigger isolation unit. Three days later, he woke up feeling sick, and was diagnosed with the disease.

"As I lay in my bed in Liberia for the following nine days, getting sicker and weaker each day, I prayed that God would help me to be faithful even in my illness," Brantly said. "Through the care of the Samaritan's Purse and SIM missionary team in Liberia, the use of an experimental drug, and the expertise and resources of the health care team at Emory University Hospital, God saved my life."

His doctors cautioned that it's unclear whether the drug or a blood transfusion Brantly got from a young Ebola survivor in Africa was helpful or hurtful. The drug is so novel that it hasn't been tested in people, and might not have made any difference at all.

"Experimental means exactly that. They are the very first individuals to have received this treatment and frankly we do not know," Ribner said.

Both patients were discharged after their medical team made sure they won't infect others. Their blood tested clean of the virus, which is spread only through direct contact with the bodily fluids of sick people experiencing symptoms. Ebola survivors generally are not contagious once they've recovered.

Still, both families asked for time alone to recover fully. David Writebol said in a statement that his wife is recuperating at an undisclosed location, and is "greatly encouraged knowing that there were so many people around the world lifting prayers to God for her return to health."

Neither survivor is saying what they'll do next. Ribner said there's no concern of a relapse, "and in fact we would anticipate immunity from this virus if they were treating patients during this outbreak."

There is a huge gap between the top-flight care these Americans got at Emory, where a crew of five infectious disease experts and 21 nurses provided rigorous care, and West Africa, where the virus has killed more than 1,300 people and counting, and even such basics as sterile fluids can be in short supply.

Ribner said he has "no clue how much they might have spent" saving the missionaries' lives, but he insisted that bringing them to Atlanta "was the right decision" and said the hospital could decide to take more Ebola patients on a case by case basis, if they are strong enough to survive the long trip.

"We cannot let our fears dictate our actions," Ribner said. "We must all care. As grateful as we are today, our work is far from over."

Treating these two patients has already given doctors insights into how to better care for Ebola patients anywhere. For example, they now believe common fluid-replacement measures may not have enough of certain nutrients patients need to recover. Emory physicians say they have begun sharing their findings to other doctors, and hope to publish in a medical journal.

At least 2,473 people have been sickened in this outbreak — more than the caseloads of all the previous two-dozen Ebola outbreaks combined, according to the World Health Organization.

Before he left the hospital, Brantly appealed to help those he left behind.

"Please continue to pray for Liberia and the people of West Africa, and encourage those in positions of leadership and influence to do everything possible to bring this Ebola outbreak to an end.

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Associated Press writer Jeff Martin contributed to this report.