Story highlights

A "close contact" of the nurse is being monitored, says CDC

The worker helped care for an Ebola patient multiple times, CDC director says

He says there was a breach in protocol and his agency is investigating

Nurse was wearing protective gear when she helped care for Thomas Eric Duncan

(CNN) —  

The deadly Ebola virus has been contracted by someone inside the United States for the first time.

A nurse who had worn protective gear during her “extensive contact” at a Dallas hospital with an Ebola patient who died tested positive during a preliminary blood test, officials said Sunday.

The woman had on a gown, gloves, mask and a shield during her multiple visits with Thomas Eric Duncan, but there was a breach in protocol, health officials said.

The patient is a nurse at Texas Health Presbyterian Hospital in Dallas, an official who is familiar with the case told CNN.

The Centers for Disease Control and Prevention in Atlanta conducted testing on the blood sample, and confirmed the results Sunday, marking the first known transmission of Ebola in the United States and the second diagnosis in the country.

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She was involved in Duncan’s care after he was placed in isolation – his second trip to the hospital after coming to the United States from Liberia – said Dr. Tom Frieden, the director of the CDC.