The head of U.S. efforts to combat the spread of Ebola has called on hospitals to be vigilant for feverish patients who have recently traveled from West Africa, calling the infection of a health worker in Dallas “unacceptable.”

Tom Frieden, director of the Centers for Disease Control and Prevention (CDC), stressed the importance of checking where those arriving at a hospital may have been.

“If they have a fever, ask where they have been in the past 21 days," Frieden urged during a press conference Monday, adding that health care workers should "immediately place in isolation" anyone with a high temperature who has recently traveled to Liberia, Guinea or Sierra Leone — the three countries that have borne the brunt of the Ebola crisis.

The comments followed news Sunday that a health care worker in Dallas had become the first person to catch the disease within the United States. The female health worker, whose name has not been released, treated Liberian Thomas Eric Duncan, who had entered the Texas Health Presbyterian Hospital hospital in Dallas only to be initially sent home despite staff being told that he had flown via the Ebola-stricken country.

Duncan was later admitted and died on Oct. 8. Frieden said the infected health care worker was now "clinically stable."

The CDC is now monitoring all hospital workers who treated Duncan. Frieden says he wouldn't be surprised if another hospital worker who cared for the patient became ill. Health experts have said that Ebola patients become more contagious as the disease progresses.

Officials have not been able to pinpoint how the virus was contracted by the health care worker in Dallas, but Frieden made mention of a "detailed investigation" to figure out what could have happened. He also said officials were considering the possibility of protective equipment that would be easier to put on and take off in an effort to prevent infection from occurring when health workers remove such equipment. It remains unclear, however, if that is what occurred in this instance.

A second health worker who had contact with the health care worker and was in isolation has "no symptoms of Ebola" and has "no fever," Frieden said.

He added that authorities are in the process of interviewing every worker who may have had contact with Duncan when he was hospitalized.

"We need to consider the possibility that there could be additional cases, particularly among the health care workers who cared for the index patient when he was so ill," Frieden said, using the term CDC officials are using for Duncan.

But the incident has revived concern that U.S. hospitals may not be as impervious to the disease as previously thought.

"We have to rethink the way we address Ebola infection control," Frieden said, "because even a single infection is unacceptable."

Meanwhile, President Barack Obama was due to consult with top administration officials Monday to get the latest developments on the government's response to Ebola, following the latest developments in Texas.

The White House said Obama was meeting with senior officials Monday afternoon for an update on steps underway to ensure the national health system is prepared to deal with the disease.

The president also spoke with U.N. Secretary-General Ban Ki-moon on Monday, the White House said, with the two agreeing that the "international community must redouble their resolve and commitment to stay the course and decisively address the Ebola crisis."

Ebola is transmitted through direct contact with bodily fluids, like blood and vomit, putting health workers at particular risk. The virus is believed to have killed more than 4,000 people in West Africa, and Liberia has recorded the highest death toll.

Al Jazeera and The Associated Press