The director of the Centers for Disease Control and Prevention and other officials testified Thursday before Congress on the agency's Ebola response and to explain where things went wrong.
"As the director of CDC, one of the things I fear about Ebola is that it could spread more widely in Africa. If this were to happen, it could become a threat to our health system and the health care we give for a long time to come," Frieden said.
U.S. President Barack Obama directed his administration to respond in a "much more aggressive way" to oversee the Dallas cases and ensure that the lessons learned there are transmitted across the country. For the second day in a row, he cancelled out-of-town trips to stay in Washington and monitor the Ebola response.
Even asObama sought to calm new fears about Ebola in the U.S., he cautioned against letting them overshadow the far more urgent crisis unfolding in West Africa, where Ebola has killed more than 4,000.
On Thursday, Chinese President Xi Jinping pledged continued support for the fight against Ebola in West Africa, without specific new aid offers. China last month pledged $33 million US in assistance to Liberia, Sierra Leone and Guinea and dispatched doctors and medical supplies.
France said on Saturday, it will begin screening passengers who arrive at Paris's Charles de Gaulle airport on the once-daily flight from Guinea's capital.
In the U.S., political and public attention is focused on what happened in Dallas, with criticism from both Republican and Democratic legislators on a House subcommittee for oversight and investigations.
"It would be an understatement to say that the response to the first U.S.-based patient with Ebola has been mismanaged, causing risk to scores of additional people," said Representative Diana DeGette, the subcommittee's top Democrat.
Frieden said Wednesday that nurse Amber Joy Vinson never should have been allowed to fly on a commercial jet because she had been exposed to the virus while caring for an Ebola patient.
Vinson was being monitored closely since another nurse, Nina Pham, also involved in Ebola victim Thomas Eric Duncan's care, was diagnosed with Ebola.
Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Disease at the National Institutes of Health, told the hearing that Pham was being transferred to the NIH near Washington for treatment.
Vinson, the second nurse, has been transferred to Emory University Hospital in Atlanta near the CDC.
Dallas hospital spokesman Wendell Watson said Thursday the move is needed because so many employees are being monitored for symptoms and aren't available to work.
A CDC official cleared Vinson to board a flight from Cleveland to the Dallas area with a temperature of 37.5 C, which is below the below the agency's threshold, agency spokesman David Daigle said.
She had no symptoms, and health officials have stressed that Ebola patients are not considered contagious until they have symptoms.
Vinson was diagnosed with Ebola a day after the flight.
Duncan, who travelled to the U.S. from Liberia, originally was sent home when he went to the Dallas hospital's emergency room.He returned in an ambulance two days later. He died of Ebola on Oct. 8.
Frieden has said breaches of protocols led to the infection of the two nurses. More than 70 other health-care workers involved in Duncan's care were being monitored.
Dr. Daniel Varga, chief clinical officer at Texas Health Resources, which oversees the Dallas hospital where Duncan was treated, told the committee that hospital staff made mistakesin the diagnosis despite their best intentions, and he is "deeply sorry."
Varga admitted there was no Ebola training for staff before Duncan was admitted, although information from the CDC was distributed.
Federal officials were also asked about travel bans on the affected countries in West Africa. The chief of the U.S. Federal Aviation Administration said the U.S. is assessing whether to issue a ban on travel from West Africa on a daily basis.
Frieden and Fauci opposed travel bans, saying they aren't effective in regions with a porous border. Frieden said that without a travel ban, officials are able to collect travellers' contact information and perform temperature checks at exit and entry.
Dr. Luciana Borio of the U.S. Food and Drug Administration noted that every Ebola patient treated in the U.S. has received at least an investigational product, such as the experimental drug ZMapp.
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