Washington (AFP) - A Texas health care worker who treated an Ebola victim has tested positive for the deadly virus, dealing a blow to the global battle to stem the epidemic and sparking questions about safety precautions.

Top US health officials have said a breach of protocol was to blame for the new Ebola case -- which if confirmed would be the second diagnosed outside Africa and the first contracted on US soil.

Her case has sparked an investigation by the US Centers for Disease Control and Prevention (CDC), and a hunt for more health care workers who may have been exposed to the dangerous virus.

More than 4,000 people have died of Ebola since the start of the year -- most of them in hardest-hit Guinea, Sierra Leone and Liberia -- and the epidemic appears to be outpacing efforts to fight it.

"We are deeply concerned by the news that a health care worker in Texas has tested preliminarily positive for infection with Ebola virus," CDC chief Tom Frieden told reporters.

"We don't know what occurred in the care of the index patient, the original patient in Dallas, but at some point there was a breach in protocol and that breach in protocol resulted in this infection."

David Lakey, commissioner of the Texas Department of State Health Services, insisted that authorities were "working with extreme diligence to prevent further spread."





- 'Breach in protocol' -





The female caregiver at Texas Health Presbyterian Hospital Dallas tested positive for Ebola on Saturday in a preliminary test and is currently in the hospital, in isolation and in stable condition.

"This is not news that should bring about panic," said Dallas county judge Clay Jenkins.

But Dan Varga, the chief clinical officer for Texas Health Resources, said the woman "was following full CDC precautions" -- protective gear that would have included a mask, gown, and gloves.

Frieden said the woman had "extensive contact" with Thomas Eric Duncan, a Liberian man who died in Texas on Wednesday.

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"We are evaluating other potential health care worker exposures," said Frieden. "It is possible that other individuals were exposed."

Duncan was believed to have been infected before he left Liberia and boarded a plane to visit family in Texas.

In a bid to keep such patients from reaching US soil, New York's JFK airport on Saturday became the first in the country to launch health screenings for travelers from epidemic-hit west Africa.

Other nations have instituted similar checks.





- 'Far ahead of us' -





The latest case underlines United Nations fears and growing concerns in the United States about Ebola, for which there is no vaccine or widely available treatment.

"The virus is far ahead of us and every day the situation gets worse," the head of the United Nations' emergency Ebola mission, Anthony Banbury, told UN leaders after a tour of Liberia, Guinea and Sierra Leone.

Passengers from West Africa arriving at John F Kennedy International Airport in New York and other major US hubs in Chicago, Washington, Atlanta and Newark will have their temperatures taken, be screened for signs of illness and answer questions about possible exposure.

"Exit screening might not find every person with Ebola; however, it does not have to be perfect to help reduce the spread of Ebola," the CDC said in a statement.





- Nurse's condition improves -





In Spain, attention remained focused on 44-year-old Teresa Romero, the Madrid nurse who became the first person infected with the hemorrhagic fever 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.

Simon added however: "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."

Romero is thought to have contracted the disease in late September in a Madrid hospital while caring for a Spanish missionary infected with Ebola in Africa who later died.

Romero has said she thought she might have developed Ebola after brushing her face with a glove -- pointing to possible gaps in the safety protocols in hospitals treating Ebola patients.

Fifteen other people, mostly hospital staff as well as Romero's husband, are under observation at the Carlos III hospital where Romero is being treated. The hospital said none of them were showing any symptoms.





- Rising toll -





The World Health Organization reported 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, diarrhea, vomiting and in some cases internal and external bleeding. It is spread by contact and the exchange of bodily fluids.

The sharp rise in deaths came as the UN said aid pledges to fight the epidemic have fallen well short of the $1 billion needed.