Dr. Tom Frieden, director of the U.S. Centers for Disease Control and Prevention (CDC), said the second worker will be transferred to Emory University Hospital.
He said the worker should not have travelled on a commercial airlinebecause the individual was in a group known to have exposure to Ebola.
In a conference call with reporters, Frieden said the worker travelled to Ohio before it was known that a nurse at the hospital was sick with the Ebola virus.
The second health-care worker, who was diagnosed with Ebola on Tuesday, had been monitoring herself for symptoms of Ebola. She failed to report that her temperature had risen slightly to 37.5 C before she departed for Dallas.
The risk to passengers is considered low because she did not vomit on the flight and she was not bleeding, Frieden said. Infected Ebola patients are not considered contagious until they have symptoms.
Frieden said the CDCwill work with state and local officials to ensure that those who are being monitored do not travel by public transit.
Earlier on Wednesday, officials said a Dallas nurse took a Frontier Airlines flight before becoming ill.
She has been identified by Reuters as Amber Vinson, who cared for a patient infected with Ebola at Texas Health Presbyterian Hospital.