A Texas health-care worker has become the first person to contract Ebola on American soil, authorities say, causing concern that safety precautions taken by medical staff could be insufficient.
Senior US health officials said on Sunday a breach of protocol was to blame for the new Ebola patient - the second person infected outside Africa and the second diagnosed in the US.
The unidentified female care-giver at Texas Health Presbyterian Hospital in Dallas tested positive for Ebola on Saturday in a preliminary test and is currently in the hospital, in isolation and in stable condition.
"This development is understandably disturbing news for the patient, the patient's family and colleagues and the greater Dallas community," the US Centres for Disease Control and Prevention (CDC) said.
But the CDC insisted that any further spread into the community surrounding the Dallas hospital "can be prevented with proper public health measures".
Dan Varga, the chief clinical officer for Texas Health Resources, which runs the Texas Health Presbyterian Hospital, said the woman "was following full CDC precautions" - protective gear that would have included a mask, gown and gloves.
However, Thomas Frieden, the CDC chief, said it was clear that "at some point there was a breach in protocol and that breach in protocol resulted in this infection".
Frieden said the woman had "extensive contact" with Thomas Eric Duncan, a Liberian man who was diagnosed with Ebola in the US last month and died in Texas on Wednesday.
Duncan was believed to have been infected before he left Liberia and boarded a plane to visit family in Texas.
"We are evaluating other potential health-care worker exposures," Frieden said. "It is possible that other individuals were exposed."
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The CDC has launched an investigation, as well as a hunt for more health-care workers who may have been exposed to the dangerous virus.
Police in Dallas stood guard on Sunday outside the caregiver's apartment complex and told people not to go inside.
Officers also knocked on doors, made automated phone calls and passed out fliers to notify people within a four-block radius about the situation, although Dallas authorities assured residents the risk was confined to those who have had close contact with the two Ebola patients.
Meanwhile in Nebraska, a 33-year-old American photojournalist who became infected with Ebola while working in Liberia was continuing to show improvements, doctors said.
Against this backdrop, US customs and health officials on Saturday began taking the temperatures of passengers arriving at New York's Kennedy International Airport from Liberia, Sierra Leone and Guinea in a stepped-up screening effort.
The screenings will expand to four additional airports - New Jersey's Newark Liberty, Washington Dulles, Chicago O'Hare and Hartsfield-Jackson in Atlanta - in the coming days.
Spanish nurse's case
In Spain, attention remained focused on Sunday on 44-year-old Teresa Romero, the Madrid nurse who became the first person infected with Ebola outside of Africa.
The Spanish crisis cell set up after she fell sick said there was "reason to hope" she could recover.
"It seems the viral charge has been brought under control and is diminishing," said Fernando Simon, head of the team set up within the Health Ministry.
"We must be highly cautious since this is someone infected with Ebola whose situation remains critical and it is possible that other organs are affected."
The UN says aid pledges to fight the epidemic have fallen well short of the $1bn needed.
The World Health Organisation say 4,033 people have died from Ebola as of October 8 out of a total of 8,399 registered cases in seven countries.
Ebola causes fever, diarrhoea, vomiting and in some cases internal and external bleeding.
It is spread by contact with bodily fluids or exposure to contaminated objects such as needles.