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(CNN) -- A female nurse at Texas Health Presbyterian Hospital in Dallas has tested positive for Ebola after a preliminary test, the state's health agency said.

Confirmatory testing will be conducted Sunday by the Centers for Disease Control and Prevention in Atlanta. Test results are expected to be announced later in the day.

The nurse helped care for Thomas Eric Duncan, the first person ever diagnosed with Ebola in the United States. Duncan died Wednesday.

The nurse is in stable condition, Texas Health Resources chief clinical officer Dan Varga said.

The nurse was involved in Duncan's second visit to the hospital, when he was admitted for treatment, and was wearing protective gear as prescribed by the CDC: gown, gloves, mask and shield, Varga said.

A "close contact" of the nurse has been "proactively" placed in isolation, he added.

Case was anticipated

"We knew a second case could be a reality, and we've been preparing for this possibility," Dr. David Lakey, commissioner of the Texas Department of State Health Services, said in a statement Sunday morning.

"We are broadening our team in Dallas and working with extreme diligence to prevent further spread."

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Texas health care worker wore protective gear