NEW YORK (AP) -- The nation's top public health agency is expanding a program that tests international travelers for COVID-19 and other infectious diseases.

The Centers for Disease Control and Prevention program asks arriving international passengers to volunteer to have their noses swabbed and answer questions about their travel. The program operates at six airports and on Tuesday, the CDC said it was adding two more -- Chicago's O'Hare and Miami.

Those locations should provide more information about respiratory infections coming out of South America, Africa and Asia, particularly, CDC officials said.

"Miami and Chicago enable us to collect samples coming from areas of the world where global surveillance is not as strong as it used to be," said the CDC's Allison Taylor Walker. "What we really need is a good view of what's happening in the world so we're prepared for the next thing."

The program began in 2021, and has been credited with detecting coronavirus variants faster than other systems. The genomic testing of traveler's nasal swabs has mainly been focused on COVID-19, but testing also is being done for two other respiratory viruses -- flu and RSV.

Participants are not notified of their results. But they are given a COVID-19 home test kit to take with them, CDC officials say.

Samples have come from more than 475,000 air travelers coming off flights from more than 135 countries, officials said.

Health officials also have been sampling wastewater that comes off international flights at a few airports. That testing is for COVID-19, but CDC officials are evaluating the possibility of monitoring wastewater for other things, Walker said.

The CDC program has a current budget of about $37 million. The agency pays two companies, Ginkgo Bioworks and XWell, to do sample collection and testing. The companies are working with CDC to grow the program to check for more than 30 different disease-causing germs.

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