During a House subcommittee hearing on Thursday, Director of the Centers for Disease Control and Prevention Thomas Frieden outlined how his agency is responding to the threat of Ebola, emphasizing the need to stop the virus "at the source." Here are key moments from that hearing. (Sarah Parnass and Ashleigh Joplin/The Washington Post)

During a House subcommittee hearing on Thursday, Director of the Centers for Disease Control and Prevention Thomas Frieden outlined how his agency is responding to the threat of Ebola, emphasizing the need to stop the virus "at the source." Here are key moments from that hearing. (Sarah Parnass and Ashleigh Joplin/The Washington Post)

Members of Congress sharply questioned top public health officials Thursday about banning travel from West African countries where the Ebola virus is out of control to the United States, demanding to know why the administration has not adopted that tactic.

“It’s not a drill,” said Rep. Fred Upton (R-Mich.), a member of the of the House Energy and Commerce oversight and investigations subcommittee, which held Thursday’s hearing. “People’s lives are at stake, and the response so far has been unacceptable.”

Thomas Frieden, director of the Centers for Disease Control and Prevention, and other officials outlined the argument for allowing travel to continue, insisting that a ban would prompt travelers to sneak into the country and make it more difficult to keep tabs on people who become sick. But Frieden did not rule out a travel ban.

“Right now, we are able to track everyone who comes in,” he said. But he added: “We will consider any options to better protect Americans.”

The hearing came as the National Institutes of Health announced that a nurse infected with the Ebola virus while caring for a patient in Dallas would be transferred to the agency’s clinical center in Bethesda, one of four locations in the United States with a special biocontainment unit.

1 of 84 Full Screen Autoplay Close Nov. 1, 2014 Oct. 31, 2014 Oct. 30, 2014 Oct. 29, 2014 Oct. 28, 2014 Oct. 26, 2014 Oct. 25, 2014 Oct. 24, 2014 Oct. 20, 2014 Oct. 18, 2014 Oct. 17, 2014 Oct. 16, 2014 Oct. 15, 2014 Oct. 13, 2014 Monday Oct. 12, 2014 Sunday Oct. 11, 2014 Saturday Skip Ad × New Ebola case in Dallas View Photos A second health-care worker at the hospital where a Liberian man died of Ebola has tested positive for the virus. Caption A surgeon working in Sierra Leone has been diagnosed with Ebola and was flown to the United States for treatment. In this April 2014 photo provided by the United Methodist News Service shows Dr. Martin Salia, who tested positive for Ebola, at the United Methodist Church's Kissy Hospital outside Freetown, Sierra Leone. Salia was flown to the Nebraska Medical Center in Omaha, Neb. for treatment. Mike Dubose/AP Buy Photo Wait 1 second to continue.

The nurse, Nina Pham, was flown Thursday evening to Frederick Municipal Airport in Frederick, Md., in an executive jet to be moved to the NIH facility, the Associated Press reported.

Anthony Fauci, director of NIH’s National Institute of Allergy and Infectious Diseases, who testified at the hearing, said Pham would receive “state-of-the-art care.” Officials at Texas Health Presbyterian Hospital Dallas, where Pham became infected, said she was in good condition.

Pham, 26, is one of two nurses at the hospital who contracted Ebola while treating Thomas Eric Duncan, a Liberian who arrived in Dallas with the virus. The other, Amber Vinson, 29, has been transferred to Emory University Hospital in Atlanta.

The Dallas hospital said that much of its intensive-care staff is “sidelined for continuous monitoring” after caring for Duncan, who died Oct. 8.

The nurses are the first two victims of Ebola transmission on U.S. soil during the current outbreak, by far the largest on record. According to the World Health Organization, there have been 8,997 confirmed, probable or suspected cases in seven countries, the vast majority of them in Liberia, Sierra Leone and Guinea. The virus has killed 4,493 people, all but a handful in the three West African nations.

The Dallas hospital apologized Thursday for its initial misdiagnosis of Duncan, who flew from Liberia to Texas and was originally sent home from the emergency room before being diagnosed with Ebola five days later.

Daniel Varga, chief clinical officer of the system that oversees the facility, told the committee that the hospital “did not correctly diagnose his symptoms as those of Ebola” and is “deeply sorry.”

View Graphic Widespread concerns for Ebola epidemic in the United States

Also Thursday, Washington’s top local health official said he has begun to limit public information about patients who show up at hospitals with Ebola-like symptoms to limit rumors.

D.C. Health Director Joxel Garcia said 12 patients who had traveled to West Africa recently had developed symptoms and had been isolated and monitored. Ebola has been ruled out, Garcia said.

Thursday’s hearing came a day after a stream of bad news. Vinson’s infection was announced Wednesday morning, followed later by the revelation that the CDC had allowed her to fly on a commercial aircraft after she called the agency to say she had a fever.

Upton was particularly critical of the decision to allow the nurse to fly back to Dallas from Cleveland. The CDC’s Frieden said that although the nurse had contacted the CDC before traveling, he was not clear on exactly what the conversation entailed and believed she had reported no symptoms to the agency.

More than 130 of Vinson’s fellow passengers on the Frontier Airlines flight from Cleveland to Dallas-Fort Worth on Oct. 13 are being screened for possible exposure to Ebola. And on Thursday, the CDC said it would also screen passengers on Vinson’s earlier flight to Cleveland on Oct. 10.

Frieden stressed that the risk here cannot be fully eliminated until the outbreak is stanched in West Africa. The idea of a travel ban has been discussed by politicians since the days after Duncan’s diagnosis. House Speaker John A. Boehner (R-Ohio) and other lawmakers are calling for a ban on travelers from Guinea, Liberia and Sierra Leone. About 150 people arrive in the United States from these countries each day, the majority of them via five airports in or around New York, Washington, Chicago and Atlanta.

Enhanced screening meant to check these travelers began last week at New York’s John F. Kennedy International Airport and expanded Thursday to four other airports, including Dulles International Airport.

In response to mounting concerns over Ebola, President Obama canceled travel Wednesday and Thursday to remain in Washington and monitor the government’s response.

Aaron Davis contributed to this report.