Washington - With no new Ebola cases in five days, US authorities were cautious but hopeful Monday that the virus has been contained in the United States after a flawed response revealed shortcomings in the system.
The fiancée of a Liberian man who died of Ebola earlier this month in Dallas, Texas was among nearly 50 people who emerged from three weeks of quarantine without any signs of illness from exposure to the virus that has killed more than 4 500 in West Africa since the beginning of this year.
About 100 more people, most of them health care workers, are being tracked in Texas after coming in contact with the first patient diagnosed in the United States in late September.
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Still, officials said it was reassuring that no new infections had emerged in recent days.
"We are breathing a little bit easier, but we are still holding our breath," said Dallas Mayor Mike Rawlings.
Those who are no longer in danger include a group of health care workers and community members who may have had contact with the Liberian man, Thomas Eric Duncan, between 24 September when he began showing symptoms and 28 September when he was isolated in a Dallas hospital.
"This is a crucial milestone for the city of Dallas and for concerned persons across the United States," said Mark Rupp, an infectious disease specialist at Nebraska Medical Center, which has treated two US Ebola patients after they were infected in Liberia this year.
"I hope this reinforces the message that the public is safe and that Ebola is not very infectious in its early stages."
Two nurses in the intensive care unit at Texas Health Presbyterian Hospital Dallas were infected while caring for Duncan, who died 8 October.
Nina Pham's infection was announced 12 October, and her colleague Amber Vinson's was three days later.
Ebola is spread though close contact with vomit, blood, diarrhoea or other bodily fluids. Most people get sick within eight to 10 days of exposure, and health care workers are particularly at risk.
Word of the nurses' infections sowed panic across the United States, leading to a rash of suspected cases that turned out to be nothing more than common illnesses.
"In the United States, two people have gotten infected with Ebola. Both of them were taking care of a desperately ill patient in a risky situation," said Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases, during a forum at Washington's Newseum.
"You have to distinguish the two nurses... from the risk to the general public who aren't anywhere near an Ebola patient, much less a very sick Ebola patient."
Pham is in fair condition at a specialised government hospital near the US capital, and Fauci declined to speculate on whether she would make a full recovery.
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"She still is a bit knocked out," Fauci said.
"When you get an infection as serious as Ebola it is very, very draining on you."
Vinson's family said in a statement they "remain intensely prayerful and optimistic about Amber's condition and of the treatment she is currently receiving" at Emory University Healthcare, in Atlanta Georgia, but gave no details on the state of her health.
The Dallas hospital which initially sent Duncan away when he sought care for pain and a fever, apologised on Sunday for its management of the case.
"As an institution, we made mistakes in handling this very difficult challenge," Texas Health CEO Barclay Berdan said in a statement.
Jesse Goodman, a doctor and public health expert at Georgetown University, said the United States was learning from the initially flawed response.
"I do think events indicate how important it is to probably be over cautious rather than over confident," Goodman said.
To that end, US health authorities on Monday issued stricter guidelines for protecting health care workers against Ebola.
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The new instructions "provide an increased margin of safety," said the US Centres for Disease Control and Prevention chief Tom Frieden.
Prior to working with an Ebola patient, medical personnel must be trained and able to demonstrate competency in putting on and taking off personal protective equipment, said Frieden.
The gear should allow no skin exposure and should include gloves, a waterproof gown or coveralls, a respirator, a face shield and a disposable hood.
Meanwhile, fears loomed that the epidemic could intensify in hardest-hit Liberia, Sierra Leone and Guinea, as the death toll continued to climb amid funding shortfalls.
Fauci said the epidemic was far from ending in West Africa, and said all nations need to pour resources into ending the spread of the disease there.
"Right now I don't think we can predict when this epidemic is going to be over. When you look at it, it is still escalating rather than declining."