The United States on Saturday stepped up its efforts to stop the spread of the deadly Ebola virus, implementing additional screenings for airline passengers from West Africa to New York’s Kennedy airport.

Public health workers at John F. Kennedy International Airport will use no-touch thermometers to take the temperatures of travelers from the three countries hit hardest by the virus -- Liberia, Sierra Leone and Guinea.

The program will be expanded over the next week to Newark’s Liberty, Washington’s Dulles, Chicago’s O'Hare and Atlanta’s Hartsfield-Jackson airports.

Officials say roughly 150 people travel daily to the U.S. from or through the three countries and that nearly 95 percent of them land first at one of the five airports at which screenings are being increased.

In addition to temperatures being taking, those who have a fever will be interviewed to determine whether they may have had contact with someone infected with Ebola. There also are quarantine areas at each of the five airports that can be used if necessary.

The recent outbreak of the virus has so far killed more than 4,000 people.

There are no direct flights to the U.S. from the three countries, but Department of Homeland Security officials said last week they can track passengers back to where their trips began, even if they make several stops. Airlines from Morocco, France and Belgium are still flying in and out of West Africa.

The advanced-screening plan was announced Wednesday, the same day the first Ebola patient diagnosed in the U.S. died in a Dallas hospital. The death of 42-year-old Thomas Eric Duncan exposed gaps in the nation's defenses against the disease and set off a scramble to track down anyone exposed to him. Duncan died about a week after arriving from Liberia and had been kept in isolation since Sept. 28.

The advanced screenings are a joint effort between the Centers for Disease Control and Prevention and the Department of Homeland Security’s Customs and Border Protection.

In the 12 months ending July 2014, Kennedy airport received nearly half of the travelers from the three West African countries, the agencies said.

They also said the enhanced measures complement exit-screening protocols already in place in those countries.

In the two months since the exit screenings began in the countries, 77 of 36,000 people have been denied boarding a flight. However, none of the 77 was found to have Ebola.

President Obama said Wednesday that the new screening measures are "really just belt and suspenders" to support protections already in place.

Border Patrol agents already look for people who are obviously ill, as do flight crews, in addition to passengers departing from West Africa being screened.

Health officials expect false alarms from arriving travelers who have fever from other illnesses. Ebola isn't contagious until symptoms begin, and it spreads through direct contact with the bodily fluids of patients.

The extra screenings at U.S. airports probably wouldn't have identified Duncan when he arrived last month because he had no symptoms while traveling.

Experts say the federal government has broad authority to screen passengers and quarantine them if necessary.

The CDC cited as legal authority the Commerce Clause of the Constitution, under which the government regulates trade with foreign countries. The 1944 Public Health Service Act also allows the federal government to take action to prevent communicable diseases, which include viral hemorrhagic fevers such as Ebola, from spreading into the country.

The Associated Press contributed to this report.