A possible Ebola patient arrives at the Texas Health Presbyterian Hospital on October 8, 2014 in Dallas, Texas.
Top US health authorities said Sunday a breach of protocol was to blame for the Ebola infection of a Texas health care worker who was said to have worn full protective gear.
The Dallas hospital where the woman worked said she had worn a mask, shield and gloves during her encounters with Thomas Eric Duncan, a Liberian who was diagnosed with Ebola in the United States last month and died on Wednesday.
The woman represents the first case of Ebola infection on US soil, and she is the second person to be diagnosed outside Africa. The disease has killed more than 4,000 people, nearly all of them in West Africa.
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.
"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."
The woman helped treat Duncan when he was admitted to the hospital on September 28 and had "extensive contact" with him on multiple occasions during his stay at Texas Health Presbyterian Hospital Dallas, Frieden said.
She developed a fever on Friday. Initial lab tests on Saturday showed she had a low level of Ebola virus in her system, Frieden said.
She has told hospital workers she is unaware of any breach in protocol, officials said.
A nurse in Spain who contracted Ebola, after caring for two elderly missionaries who died of the virus, at first said she did not know how she contracted it, and later said she might have touched her face with an infected glove.
"We are evaluating other potential health care worker exposures," said Frieden. "It is possible that other individuals were exposed."
The female US health worker, whose identity was not revealed, is currently in isolation and in stable condition.
A confirmation of the Ebola test by the CDC was expected later in the day.
A close contact of the health care worker — who CNN said was a female nurse, citing an unnamed official — has also been placed in isolation, officials said at a press conference.
"This is not news that should bring about panic," said Dallas county judge Clay Jenkins.
"We expected that something — that it was possible that a second person could contract the virus."
The worker's family has requested total privacy, he added.
But Dan Varga, the chief clinical officer for Texas Health Resources, said officials were "very concerned" that the worker had apparently contracted the virus despite following safety protocol.
"This individual was following full CDC precautions," he said, noting that the gear would have included a mask, gown, and gloves.
Duncan was estimated to have come in contact with 48 people before he was admitted to the hospital on September 28.
The healthcare worker was not among those 48 people, all of whom are being monitored and who have shown no symptoms of Ebola.
Anthony Fauci, head of the National Institute for Allergy and Infectious Diseases, echoed Frieden's comments.
"Certainly there has to have been an inadvertent innocent breach of the protocol of taking care of a patient within the personal protective equipment," Fauci said on ABC's This Week.
"That extremely rarely happens. We've been taking care of Ebola patients since 1976. Groups like Doctors without Borders who do that almost never have an infection because of the experience of doing this."
He said the CDC was trying to find out what the breach involved.