A second Texas nurse testing positive for the Ebola virus after taking care of a patient in Dallas had taken an airline flight one day before she reported symptoms, U.S. officials say.

The woman, identified as Amber Vinson, who worked at Texas Health Presbyterian Hospital in Dallas, had flown from Cleveland, Ohio, to Dallas/Fort Worth International Airport on a Frontier Airlines Flight Monday, Oct. 13, officials at the Centers for Disease Control and Prevention said.

The CDC says is it attempting to contact all of the 132 passengers who boarded Vinson's flight.

"Because of the proximity in time between the evening flight and first report of illness the following morning, CDC is reaching out to passengers who flew on Frontier Airlines flight 1143 Cleveland to Dallas/Fort Worth Oct. 13," it said in a statement.

Ebola is not considered contagious until symptoms are experienced.

In a statement, Frontier Airlines said Vinson, "exhibited no symptoms or sign of illness while on Flight 1143, according to the crew."

Because of protocols in place for caregivers treating Ebola patients, Vinson should not have been traveling on a commercial flight with other passengers, CDC Director Tom Frieden said.

From this point on the CDC will take steps to see no one else in a similar situation travels outside of a closed environment, he said.

At the Dallas hospital, Vinson had been involved in the treatment of Thomas Eric Duncan, a Liberian who died Oct. 8 and was the first person whose infection with the Ebola virus was diagnosed within the U.S.

The hospital had initially released Duncan despite his showing symptoms of fever and the fact he had come from West Africa, where the current Ebola outbreak has resulted in the death of more than 4,400 people.

Nina Pham, another nurse who cared for Duncan in the Dallas hospital, also became infected, the first person so affected in the United States.

She was in "improved condition today," while Vinson is "ill but clinically stable," Frieden said Wednesday.

Vinson was to be moved from a Dallas hospital to Emory University hospital in Atlanta, officials said.

Seventy-five health care workers at the Dallas hospital are being monitored for any signs of Ebola symptoms, said Dr. Daniel Varga, chief clinical officer of Texas Health Resources.

Frontier Airlines said customers who may have traveled on Vinson's flight should contact the CDC at 1-800-CDC-INFO.

After it was informed of Vinson's illness, the airline said, the aircraft she flew on was removed from service.

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