Screening for the Ebola virus is to begin at Chicago's O'Hare International Airport.

Customs and health officials at O'Hare will take the temperatures of passengers from three West African countries starting Thursday.

Federal health officials say the entry screenings add another layer of protection to halt the spread of the Ebola virus that has killed thousands. Screeners will use no-touch thermometers to try to find passengers with fevers.

Customs officials say about 150 people travel daily from or through Liberia, Sierra Leone or Guinea to the United States. Nearly 95 percent of them land first at airports in New York, Chicago, Newark, Atlanta or Washington, D.C.

Health officials say they expect false alarms from travelers who have fever from other illnesses. Ebola isn't contagious until symptoms begin.

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