Declaring his cure a miracle, a doctor infected with the Ebola virus while working to save patients in West Africa walked out of an Atlanta hospital on Thursday. Hospital officials said they released a colleague quietly on Tuesday at her request.

"Today is a miraculous day. I am thrilled to be alive, to be well and to be reunited with my family," Dr. Kent Brantly, 33, of Christian aid organization Samaritan’s Purse, told a news conference.

Nancy Writebol, 59, an aid worker who also contracted Ebola while doing missionary aid work in Liberia, was discharged from the hospital on Tuesday, according to Emory and the aid group SIM. She is spending private time with her husband. "As she walked out of her isolation room, all she could say was 'To God be the glory,'" Brantly said.

Brantly, who clutched the hand of his wife, Amber, before speaking, said he would be spending a month in private with his family before sharing any more of his story. "But for now we need some time together after a month apart," he said.

"Please do not stop praying for the people of Liberia and West Africa and for an end to this Ebola epidemic," Brantly pleaded in a brief statement. He hugged his doctors and nurses as he left, and officials at Emory and the CDC emphasized that the patients pose no risk to public health.

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“After a rigorous course of treatment and testing, the Emory Healthcare team has determined that both patients have recovered from the Ebola virus and can return to their families and community without concern for spreading this infection to others,” Dr. Bruce Ribner, director of Emory’s Infectious Disease Unit, said at the news conference.

"We understand that there are a lot of questions and concerns about the Ebola virus and the infection that is causes. However we cannot let our fears dictate our actions," Ribner added. "We don't think he's contagious."

Franklin Graham, president of Samaritan's Purse, said Thursday that he had "marveled at Dr. Brantly's courageous spirit as he has fought this horrible virus" and thanked staff at the hospital. On Friday, Brantly released a statement asking that people "continue to pray for and bring attention to those suffering in the ongoing Ebola crisis in West Africa." More than 1,300 people have died from the disease in the region, according to the World Health Organization, which has declared the Ebola epidemic a global health emergency.

Both Americans received experimental treatment before being flown to an isolation unit in Emory University Hospital in Atlanta in early August. Ribner says there is no way to tell if it helped. "They are the very first individuals to ever receive this agent ... and frankly, we do not no whether it helped them, whether it made no difference or whether it delayed their recovery," he said.

Ribner said doctors would follow up on both Writebol and Brantly to make sure they continue to recover, and to watch for any side-effects from the treatment. They will almost certainly be immune to this particular strain of Ebola but it's not clear what immunity they may have to other, related strains of the virus.

In fact, both could return to Africa if their recovery continued. "We would anticipate immunity to this virus so that they would probably not be at risk of infection if they were caring for patients with Ebola virus disease during this outbreak," Ribner said.

The Centers for Disease Control and Prevention says there is no concern for anyone with the release of the two patients. "They no longer have Ebola virus in their blood and therefore pose no risk to household contacts or the public. There are no restrictions to the patients' activities of daily living," CDC said in a statement.

Ribner said the hospital allowed Writebol to leave quietly and privately at her request. There was no need to tell the public because she poses no threat, he said.

"Nancy is free of the virus, but the lingering effects of the battle have left her in a significantly weakened condition," her husband David Writebol said in a statement. "Thus, we decided it would be best to leave the hospital privately to be able to give her the rest and recuperation she needs at this time."

F. Brinley Bruton and Lexi Rudolph contributed to this story