While Ebola patients are not considered contagious until they have symptoms and only two people are known to have contracted the disease in the U.S., the revelations raised new alarms about whether hospitals and the public health system are equipped to handle the deadly disease.
Federal health officials were being called to testify Thursday before a congressional committee to explain where things went wrong.
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. And for the second day in a row he cancelled out-of-town trips to stay in Washington and monitor the Ebola response.
Even as the president 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.
Obama called European leaders Wednesday to discuss better co-ordination in the fight against Ebola in Sierra Leone, Liberia and Guinea and to issue a call for more money and personnel to "to bend the curve of the epidemic."
On Thursday, Chinese President Xi Jinping pledged continued support for the fight against Ebola in West Africa, but made no specific new aid offers. China last month pledged $33 million 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' Charles de Gaulle airport on the once-daily flight from Guinea's capital.
But it was Wednesday's development in Dallas that captured political and public attention in the United States.
Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, said 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.
Still, a CDC official cleared Vinson to board the Frontier Airlines flight from Cleveland to the Dallas area. Her reported temperature — 99.5 degrees — was below the threshold set by the agency and she had no symptoms, according to agency spokesman David Daigle.
Vinson was diagnosed with Ebola a day after the flight, news that sent airline stocks falling amid fears that it could dissuade people from flying. Losses of between 5 and 8 per cent were recorded before shares recovered.
Duncan, who travelled to the U.S. from Liberia, originally was sent home when he went to the Dallas hospital's emergency room only to return much sicker 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.
Republican lawmakers, including House Speaker John Boehner, increased calls for travel bans or visa suspensions from the West African countries where the disease has spread.
The oversight subcommittee of the House Energy and Commerce Committee scheduled a hearing on Ebola for Thursday with Frieden and Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health.
In prepared testimony, Fauci said Duncan's death and the infections outside of Africa of the two Dallas nurses and a nurse in Spain "intensify our concerns about this global health threat." He said two Ebola vaccines candidates were undergoing a first phase of human clinical testing this fall. But he cautioned that that scientists were still in the early stages of understanding how and Ebola infection can be treated and prevented.
Medical records provided to The Associated Press by Duncan's family showed that Vinson inserted catheters, drew blood and dealt with Duncan's body fluids. Late Wednesday, she arrived in Atlanta to be treated at Emory University Hospital.
From now on, Frieden said, no one else involved in Duncan's care will be allowed to travel "other than in a controlled environment."
On its website, the CDC says all people possibly exposed to Ebola should restrict their travels — including by avoiding commercial flights — for 21 days.
Associated Press writers Emily Schmall and Nomaan Merchant in Dallas contributed to the report.