Ebola survivor Nancy Writebol, posing in an undisclosed location on Wednesday. (SIM handout via Reuters)

Nancy Writebol believes that the experimental Ebola treatment drug ZMapp contributed to her recovery, her son said on Friday.

Days after Writebol was released from Emory University Hospital, where she had been treated in isolation for the Ebola virus disease, two of her sons, Jeremy and Brian, spoke about her remarkable recovery on NBC’s “Today Show.”

“Probably faith first, then the care at Emory and then that product had something to do with it, we think in some way,” Jeremy Writebol said when asked what his mother believed contributed to her recovery. “But certainly that supportive care at Emory was huge.”

Both Writebol and a second American, Texas doctor Kent Brantly, received ZMapp after contracting the virus while treating Ebola patients in Liberia. They were flown, days apart in early August, via “air ambulance” to a sophisticated infectious disease treatment unit at Emory. Both were discharged this week.

However, in a press conference on Thursday, Emory’s Bruce Ribner said doctors still don’t know whether ZMapp made a difference.

“Honestly, I don’t know,” said Ribner, who is the medical director of Emory’s Infectious Disease Unit. “They are the first individuals to receive this agent. We do not know whether it helped them, whether it made no difference, or if it delayed their recovery.”

Ribner said that the supportive care, particularly re-hydration and nutrient replacement that would not have been available to Writebol and Brantly in treatment facilities in Africa, made more of a difference.

During the deadliest Ebola outbreak ever in western Africa, two American missionaries received an experimental drug called ZMapp. An Ebola expert explains how ZMapp is derived and how it fights the deadly virus. (Gillian Brockell and Pamela Kirkland/The Washington Post)

Nancy Writebol was working to combat the Ebola outbreak in Liberia as a missionary with the organization SIM when she contracted the virus.

Jeremy Writebol said that his mother is resting in private with her husband David, who is also a missionary, and they are still considering returning to Africa.

“Africa is still on their heart,” Jeremy Writebol said. “And the suffering of the people in western Africa is still very deep for them.”

The successful treatment of two Ebola patients in the United States is a first. But there have been dozens of other suspected cases in the United States, all of which have so far proven to be false alarms. And only a few have required blood tests for the virus.

This week, two patients, one in California and another in New Mexico, sent blood samples to the Centers for Disease Control and Prevention for testing after returning from West African countries with Ebola-like symptoms. Both tests returned negative.

Similarly, in other countries around the world, recent travelers to West Africa are being tested for the virus if they present symptoms linked with the disease.

An Irish man who died after returning from working in Sierra Leone, one of four countries in Africa currently experiencing an outbreak, is being tested for the virus.

And in Nigeria, where the virus spread through a single traveler, the ongoing effort to find and treat people who might have been exposed has highlighted the ease with which Ebola can potentially spread.

A single Liberian-American traveler, Patrick Sawyer, who collapsed in a Lagos airport and later died in Africa’s most populous nation, infected more than a dozen others.

Most recently, the spouses of two people who had direct contact with Sawyer have contracted the virus, according to the Associated Press. They are the first cases of secondary infection in Nigeria.

Americans, however, don’t seem to be concerned about an outbreak in the U.S.

While four in 10 Americans believe that a U.S. outbreak is at least somewhat likely, most — 56 percent — believe that it is unlikely, according to a Reason-Rupe poll conducted from Aug. 6-10.