There was a “breach in protocol” that led to the second case of Ebola virus disease diagnosed in the U.S., Centers for Disease Control and Prevention Director Thomas Frieden said on CBS News’ “Face The Nation” Sunday. The health-care worker employed at Texas Health Presbyterian Hospital in Dallas became the first American to contract the disease outside West Africa. The worker was involved in the treatment of Thomas Eric Duncan, who traveled to the U.S. from Liberia.

“I think the fact that we don’t know of a breach in protocol is concerning because clearly there was a breach in protocol. We have the ability to prevent the spread of Ebola by caring safely for patients," Frieden said. During a press conference, Dan Varga, chief clinical officer and senior executive vice president of Texas Health Presbyterian, said the health-care worker wore protective equipment while treating Duncan. The worker detected a fever as part of a self-monitoring process recommended by the CDC and was identified as a female nurse by CNN.

“Individuals being monitored are required to take their temperature twice daily. As a result of that procedure, the care-giver notified the hospital of imminent arrival and was immediately admitted to the hospital in isolation. The entire process, from the patient’s self-monitoring to the admission into isolation, took less than 90 minutes. The patient’s condition is stable,” Varga said in a statement.

The Dallas Fire Department’s hazardous-materials unit notified residents and cleaned the area around the nurse’s apartment complex and will clean her apartment, CNN reported.

The CDC will conduct a second test to confirm whether the health-care worker has Ebola. After the preliminary test came back positive, the CDC was notified of the situation and began to contact and monitor individuals who may have come into contact with the nurse.