Following the death of Thomas Duncan earlier this week, the Dallas hospital that treated him announced one of its health workers has contracted the disease, the first case of transmission within the U.S. The unnamed worker is currently in isolation and health officials have begun retracing his or her steps and observing anyone he or she came in contact with.

Texas Health Presbyterian Hospital officials announced early on Sunday one of the health care workers who cared for the late Thomas Duncan had contracted the Ebola virus, according to NBC News. The hospital conducted preliminary tests, which proved positive, when the health worker reported a slight fever late Friday.

"We knew a second case could be a reality, and we've been preparing for this possibility," said Dr. David Lakey, commissioner of the Texas Department of State Health Services. "We are broadening our team in Dallas and working with extreme diligence to prevent further spread."

A statement released by the Texas Department of State Health Services added that the CDC would confirm the test results and anyone who came in contact with the infected health worker "will be monitored based on the nature of their interactions and the potential they were exposed to the virus."

Dr. Daniel Varga, chief clinical officer for Texas Health Resources, a company that manages the Dallas hospital, said the infected worker had followed "full CDC precautions," wearing a gown, gloves, a mask and a face shield, according to the Washington Post.

No one is sure how the health worker contracted the disease while wearing the protective gear and following CDC rules.

Dallas County Judge Clay Jenkins called the infected worker "a heroic person who helped provide care to Mr. Duncan." He said, "It was possible that a second person could contract the virus," but there were contingency plans in place.

Regardless, this did not prevent a potential third infection, according to the Guardian. During the press conference on Sunday, it was announced a close contact to the health worker may have contracted the disease and is in isolation.

Dallas Mayor Mike Rawlings reassured the public the city was doing all it can to prevent the curtail the disease's progress, adding that the health worker's apartment and the surrounding area had been decontaminated.