Washington (AFP) - Five US airports will begin screening the temperatures of passengers arriving from West Africa as the United States ramps up its response to a deadly Ebola outbreak, officials said Wednesday.

"The vast majority of people" coming from Guinea, Liberia and Sierra Leone -- the three countries hit hardest by the epidemic -- will be screened, White House spokesman Josh Earnest said.

The airports implementing the measures are John F. Kennedy International in New York, Washington Dulles International, Chicago O'Hare International, Hartsfield-Jackson Atlanta International and Newark Liberty International in New Jersey.

Together, the five hubs are the destination for 94 percent of people traveling to the United States from the three most affected countries.

"The thing that's important for people to understand is, we continue to have a lot of confidence in the screening measures that are already in place and had been in place for some time now," Earnest said.

The announcement came just hours after the first person diagnosed with Ebola in the United States -- and the first outside the African continent -- died at a hospital in Texas.

Thomas Eric Duncan, a Liberian citizen, had traveled by plane from Liberia to Texas to visit family in September.

The Ebola epidemic has killed more than 3,400 people in Guinea, Liberia, Nigeria, Senegal and Sierra Leone so far this year, and experts warn the fatalities will continue to mount.

Already, "all outbound passengers are screened for Ebola symptoms in the affected countries," said a statement from the Centers for Disease Control and Prevention.

- Range of screening measures -

Exit screening measures include a travel health questionnaire, visual assessment for signs of illness, and body temperature checks.

"In the last two months since exit screening began in the three countries, of 36,000 people screened, 77 people were denied boarding a flight because of the health screening process," the CDC said.

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None of the 77 turned out to have Ebola, but many had malaria, which is transmitted by mosquitoes and is not contagious from person to person.

Additional CDC staff will be sent to the five US airports to help customs and border agents, who will review passports, looks for signs of illness and ask questions.

Temperatures will be taken with a non-contact thermometer by trained medical staff, the CDC said.

"If the travelers have fever, symptoms or the health questionnaire reveals possible Ebola exposure, they will be evaluated by a CDC quarantine station public health officer."

If needed, health authorities will be called to assist those who need further monitoring or evaluation.

Travelers with no symptoms, fever or known history of exposure will told to monitor their health for 21 days, which is the incubation period for Ebola.

They will "receive health information for self-monitoring, be asked to complete a daily temperature log, and be asked to provide their contact information," the CDC said.

Ebola virus is spread through close contact with the bodily fluids of an infected person, or by touching the corpse of a person who has died of Ebola, experts say.