Federal regulators are expanding their viral testing program for international travelers to Chicago and Miami as part of an effort to detect early signs of pathogens coming into the country.

Chicago’s O’Hare International Airport and Miami International Airport were added to the program due to the high volume of international travelers that come through both airports. The program monitors for COVID-19, RSV, the flu and potentially new pathogens.

According to the Centers for Disease Control and Prevention (CDC), these airports were chosen to specifically collect more samples from travelers coming from Asia, Africa and the Southern Hemisphere.

The CDC’s Traveler-based Genomic Surveillance (TGS) program launched in 2022 and currently operates at airports in Boston, Los Angeles, New York, Newark, San Francisco, Seattle and Washington.

TGS operates by taking nasal swabs from international travelers who participate voluntarily. Their participation is anonymous.

The CDC said in a statement that the program has “already spotted new COVID-19 variants weeks before any other programs in the U.S., buying critical time for CDC scientists to learn more about the variants and to adjust public health response quickly as needed.”

“Since it began in 2021, TGS has collected samples from more than 475,000 air travelers and covers flights from more than 135 countries from across the globe,” the CDC said.