WASHINGTON — President Obama said Monday that the US government is considering ordering more careful screening of airline passengers arriving from West Africa, as a nurse in Spain became the first person known to catch Ebola outside the outbreak zone.
In dealing with potential Ebola cases, Obama said, ‘‘we don’t have a lot of margin for error.’’
A critically ill Liberian man already hospitalized in the United States, Thomas Duncan, began receiving an experimental drug in Dallas. Medical workers are among the Americans waiting to find out whether they had been infected by Duncan.
There were encouraging signs for an American video journalist who returned from Liberia for treatment. Ashoka Mukpo, 33, who grew up in Providence, was able to walk off a plane in Nebraska, and his symptoms of fever and nausea appeared mild.
In Spain, the stricken nurse had been part of a team that treated two missionaries who had been flown home to Spain after becoming infected with Ebola in West Africa.
The nurse’s only symptom was a fever, but the infection was confirmed by two tests, Spanish health officials said. She was being treated in isolation, while authorities drew up a list of people she had had contact with.
The White House continued to rule out any blanket ban on travel from West Africa. People leaving the outbreak zone are being checked for fevers before they are allowed to board airplanes, but the disease’s incubation period is 21 days and symptoms could arise later.
Airline crews and border agents in the United States already watch for obviously sick passengers, but officials at a high-level meeting at the White House discussed potential options for screening passengers when they arrive in the United States as well.
Obama said the United States will be ‘‘working on protocols to do additional passenger screening both at the source and here in the United States.’’ He did not outline any details or offer a timeline for when new measures might begin.
The Obama administration maintains that the best way to protect Americans is to end the outbreak in Africa. To that end, the US military was working Monday on the first of 17 promised medical centers in Liberia and training up to 4,000 soldiers this week to help with the Ebola crisis.
The United States is equipped to stop any further cases that reach this country, said White House spokesman Josh Earnest.
‘‘The tragedy of this situation is that Ebola is rapidly spreading among populations in West Africa who don’t have that kind of medical infrastructure,’’ Earnest said.
About 350 US troops are already in Liberia, the Pentagon said, and will begin building a 25-bed field hospital for medical workers infected with Ebola. A torrential rain delayed the start of the job on Monday.
The virus has taken an especially devastating toll on health care workers, sickening or killing more than 370 in the hardest-hit countries of Liberia, Guinea, and Sierra Leone, places that already were short on doctors and nurses before Ebola.
In Dallas on Monday, Candace White, a spokeswoman for Texas Health Presbyterian Hospital, said Duncan was receiving the new antiviral drug brincidofovir after the Food and Drug Administration approved its use on an emergency basis.
Brincidofovir, made by Chimerix of Durham, N.C., is taken orally and is being tested against several common viruses. M. Michelle Berrey, chief executive of Chimerix, said the company was working closely with federal and local health officials, including the Centers for Disease Control and Prevention.
Governor Rick Perry of Texas urged the US government to begin screening air passengers arriving from Ebola-affected nations, including taking their temperatures. Perry stopped short, however, of joining some conservatives who have backed bans on travel from those countries.
Federal health officials say a travel ban could make the desperate situation worse in the afflicted countries, and Earnest said it was not under consideration.
Airlines have dealt with previous epidemics, such as the 2003 outbreak in Asia of SARS, or severe acute respiratory syndrome.