The worker at Texas Health Presbyterian Hospital was monitoring herself for symptoms, Dallas County Judge Clay Jenkins said. The unidentified woman reported a fever Tuesday. She was in isolation within 90 minutes, Jenkins said.
Health officials said the worker was among those who took care of Thomas Eric Duncan, who was diagnosed with Ebola after coming to the U.S. from Liberia. Duncan died Oct. 8.
The federal Centers for Disease Control and Prevention was conducting confirmatory testing of a preliminary Ebola test conducted late Tuesday at a state public health laboratory in Austin, Texas, which came back positive.
Emergency responders in hazardous materials suits began work before dawn Wednesday to decontaminate the Dallas apartment of the second hospital worker. Notices handed out to neighbours, advise them that "a health care worker who lives in your area has tested positive for Ebola."
It's not clear how the second health care worker contracted the virus, and authorities declined to say what position she holds at the hospital or the type of care she provided.
"We are looking at every element of our personal protection equipment and infection control in the hospital," said Dr. Daniel Varga, chief clinical officer for Texas Health Resources, which operates Texas Health Presbyterian Hospital Dallas.
Officials have said they also don't know how the first health worker, a nurse, became infected. But the second case pointed to lapses beyond how one individual may have donned and removed personal protective garb.
"An additional health care worker testing positive for Ebola is a serious concern, and the CDC has already taken active steps to minimize the risk to health care workers and the patient," the CDC said in a statement.
"What happened there (in Dallas), regardless of the reason, is not acceptable. It shouldn't have happened," Anthony Fauci, director of the Institute of Allergy and Infectious Diseases of NIH, said on MSNBC on Wednesday.
Fauci said he envisioned the CDC taking "a much more involved role" in establishing the proper training protocols for Ebola cases.
Dr. Tom Frieden, head of the CDC, has acknowledged that the government wasn't aggressive enough in managing Ebola and containing the virus as it spread from an infected patient to a nurse at a Dallas hospital.
"We could've sent a more robust hospital infection control team and been more hands-on with the hospital from day one about exactly how this should be managed," he said Tuesday.
Frieden outlined new steps this week designed to stop the spread of the disease, including the creation of an Ebola response team, increased training for health care workers nationwide and changes at the Texas hospital to minimize the risk of more infections.
"I wish we had put a team like this on the ground the day the patient — the first patient — was diagnosed. That might have prevented this infection," Frieden said.
The stark admission came as the World Health Organization projected the pace of infections accelerating in West Africa to as many as 10,000 new cases a week within two months.
Health and Human Services Secretary Sylvia Burwell, appearing Wednesday on NBC's "Today" show, sidestepped questions about whether she had complete confidence in the Texas hospital where the health care workers have been diagnosed with Ebola or whether they should be transferred to one of four specialized hospitals. "We will keep all options and considerations right now," she said.
The nation's largest nurses' union described how Duncan was left in an open area of the emergency room for hours. National Nurses United, citing unidentified nurses, said staff treated Duncan for days without the correct protective gear, that hazardous waste was allowed to pile up to the ceiling and safety protocols constantly changed.
RoseAnn DeMoro, executive director of Nurses United, refused to say how many nurses made the statement about Texas Health Presbyterian Hospital, but insisted they were in a position to know what happened.
A total of 76 people at the hospital might have been exposed to Duncan, and all are being monitored for fever and other symptoms daily, Frieden said. Nurse Nina Pham contracted the virus while caring for Duncan. Health officials are monitoring 48 others who had some contact with Duncan before he was admitted the hospital where he died.
Frieden said some of the world's leading experts on how to treat Ebola and protect health care workers are in the new response team. They will review issues including how isolation rooms are laid out, what protective equipment health workers use, waste management and decontamination.
Pham, 26, became the first person to contract the disease on U.S. soil as she cared for Duncan. She released a statement Tuesday through Texas Health Presbyterian Hospital saying she was "doing well," and the hospital listed her in good condition. She has received a plasma transfusion from a doctor who recovered from the virus, and the hospital CEO said medical staff members remain hopeful about her condition.
Pham was in Duncan's room often, from the day he was placed in intensive care until the day before he died.
She and other health care workers wore protective gear, including gowns, gloves, masks and face shields — and sometimes full-body suits — when caring for Duncan. Health officials have said there was a breach in protocol that led to the infections, but they don't know where the breakdown occurred.
Among the changes announced Tuesday by Frieden was a plan to limit the number of health care workers who care for Ebola patients so they "can become more familiar and more systematic in how they put on and take off protective equipment, and they can become more comfortable in a healthy way with providing care in the isolation unit."
Associated Press Chief Medical Writer Marilynn Marchione and AP reporters Martha Mendoza, Maud Beelman, Matt Sedensky and Alex Sanz in Dallas contributed to this report.