WASHINGTON (AP) — The first person diagnosed with Ebola in the U.S. died Wednesday despite intense but delayed treatment, and the government announced it was expanding airport examinations to guard against the spread of the deadly disease.

The checks will include taking the temperatures of hundreds of travelers arriving from West Africa at five major American airports.

The new screenings will begin Saturday at New York’s JFK International Airport and then expand to Washington Dulles and the international airports in Atlanta, Chicago and Newark. An estimated 150 people per day will be checked, using high-tech thermometers that don’t touch the skin.

The White House said the fever checks would reach more than 9 out of 10 travelers to the U.S. from the three heaviest-hit countries: Liberia, Sierra Leone and Guinea.

President Barack Obama called the measures “really just belt and suspenders” to support protections already in place. Border Patrol agents now look for people who are obviously ill, as do flight crews, and in those cases the Centers for Disease Control and Prevention is notified.

It’s unlikely a fever check would have spotted Thomas Eric Duncan, the Liberian man who died of Ebola in a Dallas hospital Wednesday morning. Duncan wasn’t yet showing symptoms when he arrived in the U.S.

A delay in diagnosing and treating Duncan, and the infection of a nurse who treated an Ebola patient in Spain, have raised worries about Western nations’ ability to stop the disease that has killed at least 3,800 people in West Africa.

Speaking by teleconference with mayors and local officials, Obama said he was confident the U.S. could prevent an outbreak, but he warned them to be vigilant.

“As we saw in Dallas, we don’t have a lot of margin for error,” Obama said. “If we don’t follow protocols and procedures that are put in place, then we’re putting folks in our communities at risk.”

Health workers are especially vulnerable to Ebola, which isn’t airborne like the flu but is spread by contact with the bodily fluids of infected people.

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