US health authorities have confirmed preliminary results showing a Texas doctor who treated Liberian Ebola victim Thomas Eric Duncan has herself contracted the virus.
Mr Duncan succumbed to the virus last week and Texas Health Resource spokesman David Varga said the health worker began showing symptoms shortly after.
"Last Saturday evening, a preliminary blood test on a care giver at Texas Health Presbyterian Hospital Dallas proved positive for Ebola," Dr Varga said.
"This health care worker had been under the self-monitoring regimen prescribed by the CDC and based on involvement in caring for the patient Thomas Eric Duncan during his care that started on September 28."
If confirmed by further testing, it would be just the second diagnosed case outside Africa and the first contracted on US soil.
Dr Varga said the female doctor's condition is stable and that a close contact of hers has also been placed in isolation as a precautionary measure.
He told reporters he was concerned the infection occurred despite the use of protective medical equipment and clothing, including a gown, gloves, mask and shield.
The case has sparked an investigation by the US Centres for Disease Control and Prevention (CDC) and a hunt for more health care workers who may have been exposed to the deadly virus.
CDC spokesman Thomas Frieden said 48 other people who may also have had contact are being observed.
Dr Frieden said that at some point during the care of the original patient there was a breach in protocol which resulted in the infection of the healthcare worker.
"Unfortunately, in the coming days we may see additional cases of Ebola," he said.
"This is because the health care workers who cared for this individual may have had a breach of the same nature as the individual who appears now to have had a preliminary positive test. That risk is in the 48 people who are being monitored all of whom have been tested daily, none of whom so far have developed symptoms or fever."
Dr Frieden said a program to ramp up the education and training of health care workers to deal with Ebola at the Texas hospital has already begun.
He said the CDC is also recommending the number of workers who care for Ebola patients be kept to an absolute minimum.
"The two areas where we will be looking particularly closely is the performance of kidney dialysis and respiratory intubation," he said.
"Both of those procedures may spread contaminated materials and are considered high-risk procedures."
The White House said President Barack Obama has been briefed and has asked federal authorities to take additional steps to ensure the American medical system is prepared to follow the correct protocols in dealing with Ebola.
The CDC admits the infection of a second person with Ebola is "disturbing news" for the Dallas community, but Dr Frieden said health authorities remain confident any further spread of the virus can be prevented.
These kinds of reassurances haven't managed to stave off global concern of the virus' spread, with infections being recorded in seven countries so far.
More than 4000 people have died during the epidemic, the vast majority in the West African countries Liberia, Guinea and Sierra Leone.
In Spain, a nurse being treated for Ebola remains in a critical condition, but her doctors in Madrid insist there is still hope she can recover.
Spanish health authorities said 44-year-old nurse Teresa Romero is conscious and sitting unaided, as three more people joined 12 others hospitalized in Madrid for monitoring.
Meanwhile, an Australian nurse who sparked an Ebola scare has left hospital in Cairns after a second round of tests came back negative.
A Cairns Hospital spokesman said Sue Ellen Kovack went home early this morning.
The 57-year-old recently returned from Sierra Leone where she had been treating Ebola victims.
