Dr. Kent Brantly and his wife, Amber, are seen in an undated photo provided by Samaritan's Purse. Brantly became the first person infected with Ebola to be brought to the United States from Africa, arriving at at Emory University Hospital, in Atlanta on Saturday, Aug. 2, 2014. Fellow aid worker Nancy Writebol was expected to arrive in several days. (AP Photo/Samaritan's Purse)

The second American aid worker recently diagnosed with Ebola in west Africa is en route to Atlanta.

A chartered plane specially equipped to contain took off at 1:12 a.m. local time (9:12 p.m. EDT Monday) from the airport in Liberia's capital, Monrovia. An Associated Press reporter saw the four-vehicle convoy arrive at the airport.

Although hospital officials haven't released the patient's identity, the aid group she was working with has identified her as 59-year-old Nancy Writebol.

Writebol will be treated at a special isolation unit at Emory University Hospital in Atlanta. Dr. Kent Brantly was taken to the unit Saturday after arriving from Liberia aboard the same aircraft.

Brantly and Writebol contracted Ebola while treating patients at a missionary clinic in Liberia.

Both are being treated with an experimental drug never tested for safety in humans.

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