At this point, incoming travelers from West Africa get fact sheets about the disease, but aren’t specifically tested for a fever or asked if they had contact with someone who had the disease. Duncan was asymptomatic while traveling. The New York Times reported that while he was in Africa he accompanied a neighbor to the hospital in a taxi who later died of the disease.

40,000 Passengers

The U.S. has had more than 40,000 visitors from West Africa in the past six months, according to Frieden. Most connect to the U.S. through European airports. U.S. officials have also helped each of the three nations with Ebola outbreaks, Liberia, Sierra Leone and Guinea, set up screening programs at their airports to identify passengers with fevers or other symptoms.

“The most effective way to go about controlling this is to prevent those individuals from getting on a plane in the first place,” said Lisa Monaco, the White House homeland security and counter-terrorism adviser, said on Oct. 3. “Since these measures have been in place, dozens and dozens of people have been stopped from getting on flights in the region.”

Meanwhile, Frieden warned that cutting off travel for passengers from West Africa might fuel the outbreak and raise the possibility it spreads to other nations because it would make it harder to get aid into the countries.

Southwest Airlines

“Something we might do out of the best of intentions of Americans might actually increase Americans’ risk,” he said. It would also, “make it harder to get help in” to those nations, he said.

Southwest Airlines Co. Chief Executive Officer Gary Kelly said, “I don’t see the need to do anything differently.”

While Southwest doesn’t fly beyond the Caribbean and Mexico, it could pick up international passengers who fly into several U.S. gateways for flights across the country. The Dallas-based carrier hasn’t taken any new steps beyond “over- communicating” facts about Ebola to its employees, Kelly said after remarks at a Dallas meeting today.

“Everyone has their plans, everyone has their cleaning programs,” he said. “There are FAA standards for all of these things. It feels like its very routine. If the protocols change, we’ll have to react to that, but right now it’s business as usual.”

Critical Condition

In Dallas, Duncan is now in critical condition at a hospital and people who came into contact with him are being monitored for symptoms. Frieden said that this example shows that while there may be isolated cases of the disease in the U.S., “I remain quite confident we will not have a widespread outbreak.”

“We will stop it in its tracks because we’ve got infection control in hospitals, and public health that tracks and isolates people if they get symptoms,” he said on ABC’s “This Week” yesterday. “But we have to recognize that, try as we might, until the outbreak is controlled in Africa, we can’t get the risk here to zero.”

--With assistance from Mary Schlangenstein in Dallas.

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