WASHINGTON — Anyone flying to the United States from Ebola-affected countries in West Africa must enter through one of five airports screening for the disease, Jeh C. Johnson, the Homeland Security secretary, said Tuesday as the Obama administration stepped up precautions to stop the spread of the virus.

The government had already instituted temperature checks for West Africans arriving at Kennedy International in New York, Newark Liberty International, Washington Dulles International, O’Hare International in Chicago, and Hartsfield-Jackson International in Atlanta. The five airports already account for 94 percent of all arrivals from the affected countries — Liberia, Sierra Leone and Guinea. A fever is one symptom of the disease and an indication that the person could be contagious.

Mr. Johnson said airlines were working to reroute passengers who had been scheduled to arrive at other airports. Some members of Congress have been pressing for a travel ban from those countries.

Senator Charles E. Schumer of New York called the move a “good and effective step” toward protecting Americans.