A second case of Ebola has been identified in the United States, following the death of the first person diagnosed with the disease.

Early Sunday, Texas health officials announced that one of the nurses who tended the Ebola patient at the Texas Health Presbyterian Hospital in Dallas had fallen ill and tested positive in a preliminary test for the fast-killing disease.

“Confirmatory testing will be conducted by the Centers for Disease Control and Prevention in Atlanta,” a news release from the Texas Department of State Health Services states.

From USA Today:

The care-giver reported having a fever Friday night and was hospitalized, isolated and referred for testing within 90 minutes, Clay Jenkins, Dallas County’s chief executive and its Homeland Security director, said at a news conference.

“While this is obviously bad news, it is not news that should bring about panic,” Jenkins said. “We knew it was a possibility that a second person would contract the virus. We had a contingency plan in place.”

It is still unknown how the unnamed female healthcare worker contracted the virus. According to chief clinical officer at the hospital Daniel Varga, full protective gear was donned when she treated Duncan.

The fact that the virus was transmitted even though the nurse wore protective clothing points to a breach in protocol, says CDC head Tom Frieden.

“Clearly there was a breach in protocol,” Frieden said this morning in an interview with CBS’ Face the Nation. “We have the ability to prevent the spread of Ebola by caring safely for patients … We’ll conduct a full investigation of what happens before health workers go in, what happens when they’re there, and what happens in the taking out, taking off their protective equipment because infections only occur when there’s a breach in protocol.”

The diagnosis comes merely four days after the death of Ebola victim Thomas Eric Duncan, who was the first person diagnosed with the disease within the United States.

Duncan was admitted to hospital on September 30, complaining of a 103-degree fever, headache and abdominal pain. He died on October 8.

Update (1:00PM CT): A team of epidemiologists and health investigators are questioning people within a four-block radius of the home of the Dallas healthcare worker who tested positive for Ebola Sunday.

At least one of the nurse’s “close contacts” has been placed in isolation.

Additionally, a dog that was inside the woman’s apartment is being monitored, though it currently shows no symptoms of the Ebola virus.

“Dallas Mayor Mike Rawling said the hazardous materials unit of the Dallas Fire Department has cleaned up and decontaminated the shared areas of her apartment complex,” reports the Daily Mail.

“Hazardous materials units have also cleaned out the nurse’s car.”