President Barack Obama urged Americans on Saturday not to succumb to hysteria about Ebola, amid three cases nationwide in a global pandemic that has infected over 9,000 in West Africa.

Obama also remained adamant in his weekly radio address that he is not planning to give in to demands from some lawmakers for a ban on travelers from the worst-hit countries, including Liberia, Sierra Leone and Guinea.

Obama, whose approval rating is already low, has been criticized over his administration's handling of Ebola. He held a flurry of meetings on the issue in recent days and on Friday appointed Ron Klain, a lawyer with long Washington experience, to oversee the effort to contain the disease.

Obama sought to put the extent of the disease in the United States in perspective. "What we're seeing now is not an 'outbreak' or an 'epidemic' of Ebola in America," he said. "This is a serious disease, but we can't give in to hysteria or fear."

Americans' faith in the medical system and in authorities' ability to prevent the disease from spreading in the United States was jolted by a series of mis-steps after a Liberian visitor to Texas was initially not diagnosed with the illness by a Dallas hospital in late September.

The man, Thomas Eric Duncan, was admitted to Texas Health Presbyterian Hospital several days later and diagnosed with the disease. Two nurses who were part of the team caring for Duncan, who died on Oct. 8, contracted Ebola. Amber Vinson is being cared for at Atlanta's Emory University Hospital, while Nina Pham is being treated at the National Institutes of Health (NIH) just outside Washington.

Pham, whose condition was described as "fair" on Friday, continues to rest comfortably at NIH, hospital spokesman John Burklow told Reuters on Saturday.

A chain of more than 100 people who had contact with either Duncan or the sick nurses are being monitored in case they develop the disease, which has an incubation period of up to 21 days and is transmitted by contact with a sick person's bodily fluids.

Some 800 passengers who took the same planes as Vinson on a trip she made to Ohio before being diagnosed, and passengers on subsequent flights using the same planes, have been contacted by the airline, Frontier Airlines, the carrier said on Saturday.

The airline said in a letter to employees that it had been informed by the U.S. Centers for Disease Control and Prevention (CDC) that the Dallas nurse may have been in a more advanced stage of the illness than previously thought, when she traveled back to Dallas from Cleveland on Oct. 13.

The White House said late on Friday it would send senior personnel to Dallas to help federal, state and local officials there trying to identify and monitor people who came in contact with the three people who fell sick with Ebola.