DALLAS (Reuters) - A second Texas nurse who contracted Ebola flew on a commercial flight from Ohio to Texas with a slight temperature the day before she was diagnosed, health officials said on Wednesday, raising new concerns about U.S. efforts to control the disease.

Chances that other passengers on the plane were infected were very low, but the nurse should not have been traveling on the flight, U.S. Centers for Disease Control and Prevention (CDC) Director Dr. Thomas Frieden told reporters.

The woman, Amber Vinson, 29, was isolated immediately after reporting a fever on Tuesday, Texas Department of State Health Services officials said. She had treated Liberian patient Thomas Eric Duncan, who died of Ebola on Oct. 8 and was the first patient diagnosed with the virus in the United States.

Vinson, a worker at Texas Health Presbyterian Hospital in Dallas, had taken a Frontier Airlines flight from Cleveland, Ohio to Dallas/Fort Worth International Airport on Monday, officials said.

In Washington, President Barack Obama said the likelihood of a widespread Ebola outbreak was “very, very low.” But he pledged a more aggressive response to U.S. Ebola cases from federal officials and would do everything possible to ensure no more healthcare workers are infected.

Obama met with Cabinet officials to discuss the government’s response to the Ebola situation after canceling a planned political trip to New Jersey and Connecticut.

The CDC said earlier that it was asking all of the more than 130 passengers who were also on the Frontier flight to call a CDC hotline.

Government officials said Vinson was being transferred to Emory University Hospital in Atlanta, which has successfully treated two people who contracted the disease in West Africa and were flown back to the United States.

At least 4,493 people, predominantly in West Africa, have died in the worst Ebola outbreak since the disease was identified in 1976, but cases in the United States and Europe have been limited. The virus can cause fever, bleeding, vomiting and diarrhea, and spreads through contact with bodily fluids.

Frieden said Vinson had been monitoring herself for symptoms of Ebola and failed to report that her temperature had risen to 99.5 degrees Fahrenheit (37.5 degrees Celsius) before she left for Dallas.

Even so, Frieden, who has come under pressure for apparent lapses in U.S. preparedness to fight Ebola, said the risk to other passengers was “very low” because she did not vomit on the flight and was not bleeding.

A statement from the CDC and Frontier Airlines said Vinson flew out of Dallas/Fort Worth on Friday and flew back home to Dallas on Frontier Flight 1143 on Monday.

Vinson, who was visiting family in Ohio, is related to three Kent State University employees. The school’s health services director, Dr. Angela DeJulius, said the family members had been asked to remain off campus for 21 days, while monitoring themselves for possible symptoms of Ebola in line with CDC protocols.

U.S. airline stocks tumbled again on Wednesday on renewed fears of a drop-off in air travel. Ebola fears also contributed to a nearly 2 percent drop in the Dow Jones Industrial Average, which was under pressure from global economic concerns.

Over the weekend, 26-year-old nurse Nina Pham became the first person to be infected with Ebola in the United States. She had cared for Duncan during much of his 11 days in the hospital.

The hospital said on Wednesday that Pham continued to be “in good condition.”

National Nurses United, which is both a union and a professional association for U.S. nurses, said on Tuesday that the hospital lacked protocols to deal with an Ebola patient, offered no advanced training and provided nurses with insufficient gear, including suits that left their necks exposed.

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‘PILED TO THE CEILING’

Basic principles of infection control were violated by both the hospital’s Infectious Disease Department and CDC officials, the nurses said, with no one picking up hazardous waste “as it piled to the ceiling.”

“The nurses strongly feel unsupported, unprepared, lied to, and deserted to handle the situation on their own,” the statement said.

The hospital said in a statement that it had instituted measures to create a safe working environment and it was reviewing and responding to the nurses’ criticisms.

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Speaking early Wednesday on CBS “This Morning,” U.S. Health and Human Services Secretary Sylvia Burwell declined to comment on the nurses’ allegations.

Dallas Mayor Mike Rawlings said at a news conference Wednesday that the second infected nurse lived alone. He said local health officials moved quickly to clean affected areas and to alert her neighbors and friends. A decontamination could be seen taking place at her residence.

Residents at The Bend East in the Village apartment complex were awoken early Wednesday by text messages from property managers saying a neighbor had tested positive for Ebola, and pamphlets had been stuffed beneath doors and left under doormats, said a resident, who asked not to be named.

Other residents were concerned enough that they were limiting time spent outdoors.

“Everybody thinks this won’t happen because we are in the United States. But it is happening,” said Esmeralda Lazalde, who lives about a mile from where the first nurse who contracted Ebola resides.

Texas Health Presbyterian is doing everything it can to contain the virus, said Dr. Daniel Varga of Texas Health Resources, which owns the hospital. “I don’t think we have a systematic institutional problem,” he said at a news conference on Wednesday.

At the same briefing, Dallas County Judge Clay Jenkins, the county’s chief political officer, said authorities were anticipating additional possible Ebola cases.

“We are preparing contingencies for more, and that is a very real possibility,” Jenkins said.