The Centers for Disease Control and Prevention (CDC) announced Monday it will be expanding its respiratory viral surveillance of international travelers.

In 2022, the CDC launched its Traveler-based Genomic Surveillance Program (TGS), a public-private partnership to serve as an early-warning detection system at U.S. airports for COVID-19 variants.

The voluntary program involves taking nasal samples from international travelers coming into the U.S., with select positive samples being sent to the CDC.

The program is a partnership with Ginkgo Bioworks and XpresCheck. The agency will expand these efforts by testing for more than 30 other additional pathogens, including respiratory syncytial virus (RSV) and the flu.

This pilot program will launch at four U.S. airports: Kennedy International Airport, San Francisco Airport, Logan International Airport and Dulles Airport.

“The expansion of the Traveler-based Genomic Surveillance program to flu, RSV, and other pathogens is essential as we head into fall respiratory season,” Cindy Friedman, chief of CDC’s Travelers’ Health Branch, said in a statement.

“The TGS program, which began during the COVID-19 pandemic, acted as an early warning system to detect new and rare variants of the SARS-CoV-2 virus and will do the same for other respiratory viruses going forward.” Since launching last year, the TGS has enrolled more than 360,000 anonymous volunteers, covering flights from 135 countries.