The development that a Texas health care worker tested positive for Ebola after caring for a patient who died of the virus in Dallas highlights the high-stakes risks such workers face in combating Ebola's spread.

Texas officials confirmed early Sunday that the worker, who has not been identified, preliminary tested positive for the virus and was placed in isolation at Texas Health Presbyterian Hospital in Dallas. The Centers for Disease Control and Prevention (CDC) confirmed the test results Sunday afternoon.

The employee had come in contact with Thomas Eric Duncan, the man who fell ill and was treated for the virus there after traveling to Texas from his native Liberia. Duncan succumbed to the disease on Oct. 8.

The latest diagnosis raises questions about how the health care worker was exposed to Ebola, which can only be transmitted through direct contact with bodily fluids of a person showing symptoms.

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Texas officials said Sunday the employee had followed full CDC protocol for interacting with Duncan by wearing a gown, glove, mask and shield. But the head of the CDC said it appears the infection was a result of a "breach in protocol."

“The care of Ebola can be done safely, but it’s hard to do it safely," Dr. Thomas Frieden said. "It requires meticulous and scrupulous attention to infection control and even a single inadvertent, innocent slip can result in contamination."

Frieden said the CDC is investigating how the female worker, who had "extensive contact” with Duncan on multiple occasions, was exposed to the virus. He said they're looking “particularly closely” at performance of kidney dialysis and respiratory intubation on Duncan, which he characterized as "high-risk procedures" that may spread contaminated materials. Removing protective gear that may be soiled and contaminated without allowing the materials to touch your clothes or body following such procedures is "critically important and not easy to do right," he said.

Texas officials are still looking to identify the point of exposure. Dr. Daniel Varga, chief clinical officer for Texas Health Resources, said they remain "confident that the precautions we have in place are protecting our health care workers."

Health Workers Monitored for Signs of Illness

The infected health care worker was one of at least 18 employees self-monitoring for symptoms of the virus by taking a temperature twice daily. That process caught the patient's low-grade fever Friday night, leading the worker being admitted to the hospital and put in isolation in the span of 90 minutes, officials said. A close contact of that worker was also admitted as a precaution.

Additional epidemiologists and disease-detecting resources are being called upon to monitor the health workers who may have been exposed. Frieden said the CDC is closely watching all workers who came in contact with Duncan and will continue to ramp up safety training and education for hospital employees. The CDC is also recommending that the facility minimize the number of employees who come in contact with Ebola patients and assign someone to direct and supervise infectious disease containment measures full time.

While he cautioned that additional Ebola cases may surface among those exposed during the potential breach, Frieden said the CDC believes there is "no risk to people outside of the circle of health care workers who helped the patient or the possible and definite contacts we have already identified."

Heightened Risks for Health Workers

The CDC said health care workers and others caring for the sick are at "highest risk" for exposure, due to increased chance they will come in contact with fluids. Because people with Ebola "become progressively infectious the sicker they become," health professionals coming in contact with patients as their conditions worsen are especially susceptible, Frieden said.

Hundreds of such workers have fallen sick across the globe.

In late August, the World Health Organization called the "high proportion" of doctors, nurses and heath care workers infected "unprecedented." At that point, the virus had sickened more than 240 health care workers in Guinea, Liberia, Nigeria and Sierra Leone, claiming the lives of more than 120.

The first person to become infected outside of West Africa was a Spanish nurse's aid who had cared for a priest who died of the virus. One of her doctors said last week that her gloves may have touched her face when she took off her protective gear.

Two American aid workers, Dr. Kent Brantly and Nancy Writebol, also contracted the virus while caring for sickened patients in Liberia. A third, Dr. Richard Sacra, fell ill with Ebola while delivering babies there. All three survived after receiving treatment in the United States.

The heightened risks for health workers and the latest case have sparked concerns about hospitals' readiness to handle possible and confirmed Ebola cases while ensuring employee safety. A national nurses union said Sunday that it will hold a conference call for members Wednesday in response to "steady reports from nurses at multiple hospitals who are alarmed at the inadequate preparation they see at their hospitals."

"The time to act is long overdue," National Nurses United Executive Director Rose Ann DeMoro said in a statement.

Frieden said while the CDC is looking into the best practices for handling Ebola cases moving forward, including relying more heavily on specialized facilities like the one in Nebraska that treated Sacra and is currently treating an NBC freelance cameraman with the virus, it's important that all hospitals have the training and "ability to rapidly consider, isolate and diagnose people who may have Ebola."

"We can't let any hospital let its guard down," he said.