(CNN) — [Breaking news update, posted at 11:32 a.m. ET]

“The (Ebola treatment) protocols work. … But we know that even a single lapse or breach can result in infection,” Dr. Tom Frieden, the director of the Centers for Disease Control and Prevention in Atlanta, said Sunday.

According to CNN, the health care worker is a female nurse:(CNN) — [Breaking news update, posted at 10:32 a.m. ET]

An official familiar with the case told CNN that the Centers for Disease Control and Prevention will investigate to see if guidelines were followed properly.

“The CDC is looking very carefully around the circumstances of this patient’s infection and will look to see if there were any breaches and, if so, what those were,” the official said.

[Previous story, posted at 10:03 a.m. ET]

A female nurse at Texas Health Presbyterian Hospital in Dallas has tested positive for Ebola after a preliminary test, officials 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 patient is a female nurse, an official who is familiar with this case told CNN.

She helped care for Thomas Eric Duncan, the first person ever diagnosed with Ebola in the United States, Texas Health Resources chief clinical officer Dan Varga said. Duncan died Wednesday.

The nurse is in stable condition, Varga said.

BREAKING NEWS – (CNN) — A health care worker at Texas Health Presbyterian Hospital has tested positive for Ebola after a preliminary test, the hospital said in a statement.

 
Confirmatory testing will be conducted by the Centers for Disease Control and Prevention in Atlanta.  The employee [diagnosed with Ebola] helped care for Thomas Eric Duncan, the first person diagnosed with Ebola in the United States. Duncan died on Wednesday.

“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, in a statement Sunday morning.
“We are broadening our team in Dallas and working with extreme diligence to prevent further spread.”  (link)

The health care worker reported a low grade fever Friday night and was isolated and referred for testing. The preliminary ​test result was received late Saturday.  […]  Health officials have interviewed the patient and are identifying any contacts or potential exposures. People who had contact with the health care worker after symptoms emerged will be monitored based on the nature of their interactions and the potential they were exposed to the virus.   (link)