President Obama said Wednesday that he was "cautiously more optimistic" that the chances of additional infections in the U.S. stemming from Ebola victim Thomas Eric Duncan are ebbing."

"A number of things make us cautiously more optimistic about the situation here in the United States," Obama said after holding his first Oval Office meeting with newly-appointed Ebola response coordinator Ron Klain and other senior aides. "First of all, we now have seen dozens of persons who had initial interaction with Mr. Duncan, including his family and friends, and in some cases people who have had fairly significant contact with him, have now been cleared and we’re confident that they do not have Ebola."

The fact that Duncan's closest associates have not fallen ill, the president added, "just gives, I think, people one more sense of how difficult it is to get this disease... And so, once again, I want to emphasize to the public: This is not airborne; you have to have had contact with the bodily fluids of somebody who is actually showing symptoms of Ebola, which is why it makes it so hard to catch, although it obviously is very virulent if, in fact, you do come into contact with such bodily fluids."

Obama met not only with Klain but with his homeland security adviser Lisa Monaco, National Security Adviser Susan Rice, Health and Human Services Secretary Sylvia M. Burwell and the State Department’s Ebola coordinator Nancy Powell. He said "our hearts and thoughts and prayers are still with the two nurses who were affected" and he and his staff are "cautiously optimistic" about their recovery as well.

Noting that he had spoken Wednesday to co-workers of the two Texas Health Presbyterian Hospital nurses, he found that their "spirits were good."

"People were very proud of the work that they’ve done, and understandably so," the president said. "Because as I’ve said before, when it comes to taking care of us and our families, nobody is more important than the front-line health workers and nurses in particular who so often are the ones who have immediate and ongoing contact with patients."

Obama emphasized that he remained concerned about the spread of the deadly virus in Africa. The Centers for Disease Control and Prevention announced Wednesday that people who arrive in the U.D. from countries in the center of the Ebola outbreak will be monitored for 21 days by public health officials.

The White House also issued a fact sheet Wednesday afternoon outlining how the U.S. is continuing to ramp up the resources it has in West Africa to help contain the spread of the disease. The federal government has deployed more than 170 civilian medical, health-care and disaster response experts to the region, along with 600 U.S. military personnel. Another 2,600 military personnel are expected to be sent to West Africa, officials said, and personnel from the U.S. Naval Medical Research Center continue to operate three mobile medical labs.

The Pentagon is finishing construction of a hospital for infected medical workers that will be up and running by the end of the month, according to officials, and additional U.S. support has helped Liberia increase the number of safe burial teams it has operating there to 65.