Air samplers placed near customs areas at four major U.S. international airports detected COVID-19 genetic material in 98.3% of samples and influenza A in 17.2%, according to a CDC-led study in PLOS Global Public Health. The monitoring covered San Francisco International, Newark Liberty, Washington Dulles, and Dallas/Fort Worth airports from October 2023 through August 2024.
The more useful finding for public health is not how often the viruses showed up. Flu levels in the air rose and fell in step with airplane wastewater, traveler nasal swabs, and national clinical lab data, but COVID readings did not track those signals in a statistically meaningful way. The authors concluded that air sampling "can complement aviation wastewater surveillance at ports of entry," while noting that performance varies by pathogen and sample type.
For travelers, nothing changes at the gate. The samples were collected in 2023 and 2024, they detect viral genetic material rather than proving an infectious virus was present, and they cannot identify any passenger. What the study offers is a look at how federal health officials are building early warning systems where new strains are likely to enter the country.
Flu Signals Matched, COVID Signals Did Not
The samplers ran 10 hours a day on tables about 28 to 30 inches off the floor, in areas next to customs and immigration inspection and near several hundred arriving international passengers. Of 460 usable samples, 452 contained SARS-CoV-2, the virus that causes COVID-19, and 79 contained influenza A. Flu turned up weekly from January 1 to March 18, 2024, appeared sporadically until April 22, and then disappeared, mirroring that winter's flu season.
At San Francisco and Dulles, where the CDC also collected airplane wastewater and voluntary nasal swabs, flu in the air correlated strongly with national clinical testing and traveler swabs and moderately with wastewater. COVID appeared in nearly every sample, which made rises and falls hard to see. The authors suggested flu's more seasonal pattern and lower background levels made it easier to track.
Genetic sequencing still proved useful for COVID. Air samples captured the same variant shifts seen nationally, including the decline of JN.1 and the rise of KP.2 and KP.3. However, airplane wastewater picked up those KP variants about six weeks earlier than the air samplers did, though the authors noted the timing varied by type of wastewater sample. Wastewater reflects only travelers who use an airplane lavatory, while air sampling can capture people who never do. Broader sequencing of a subset of samples identified 30 virus species, including RSV and influenza B.
Inside the Terminals at SFO, Newark, Dulles and DFW
Detection rates varied by airport. Influenza A appeared in 25.7% of San Francisco samples, 17.8% at Dallas/Fort Worth, 15.9% at Newark and 8.3% at Dulles, while COVID was found in at least 97.5% of samples at every site. San Francisco added a second sampler in June 2024, and Dallas/Fort Worth sampled only from February to August 2024, so the sites are not perfectly comparable. The paper does not explain the differences between airports, and the authors said sampler placement, airflow, and passenger movement need more study.
The air study sits within the CDC's Traveler-Based Genomic Surveillance program, a public-private partnership that monitors arriving international travelers at select airports. The program collects anonymous, voluntary nasal swabs at airports in Miami, Newark, Seattle, San Francisco, Washington and New York's JFK. It tests airplane wastewater at sites including Boston, Los Angeles, San Francisco, Washington and JFK.
Those locations matter for residents of the Bay Area, the New York and New Jersey region, greater Washington, and North Texas. U.S. airports are visited by more than 1 billion travelers each year, according to the CDC, and a new variant or flu strain arriving on an international flight can reach nearby communities before local clinics see it.
Limits Travelers Should Keep in Mind
The researchers were direct about the method's weak spots. Terminal air comes from a mix of airport staff, domestic passengers, and visitors, not only arriving international travelers. "This limitation reduces the specificity of air sampling for monitoring pathogen importation," the authors wrote. Sampling times were not fully standardized, and low amounts of genetic material made some sequencing difficult.
The work was a CDC surveillance activity, but seven authors were employed by Ginkgo Bioworks, a CDC partner in the traveler program, and held or received equity in the company. Two University of Wisconsin–Madison authors are managing partners of a consultancy that advises on environmental monitoring. The study is peer-reviewed, and its sequencing data are public, but those commercial ties are worth knowing.
Current conditions are a separate question. The CDC's latest respiratory illness data update shows COVID activity elevated and increasing nationally while hospitalizations remain low, with flu and RSV activity low as of September 18. Travelers can also check local levels on the CDC's COVID wastewater data page before a trip.
The practical steps are familiar ones. People with fever, cough, or sore throat should consider delaying travel or wearing a mask, and anyone planning to visit an older relative or someone with a weakened immune system can test before going. Trouble breathing, chest pain or new confusion call for urgent care, and people at higher risk can ask a clinician or pharmacist which fall vaccines are recommended for them.
The study cannot show whether the detected virus was infectious, whether air sampling will expand to more airports or what it would cost at scale. The authors called for more work on detection limits, sampler placement, and clear triggers for public health action. The CDC updates its respiratory data on Fridays, and MedicalDaily will follow any expansion of airport air monitoring.
Key Questions Answered
What did the airport study find? Air samplers near customs areas at four airports detected COVID genetic material in 98.3% of samples and influenza A in 17.2%. Flu trends in the air matched other surveillance data, while COVID trends did not.
Which airports were involved? The study covered San Francisco International, Newark Liberty, Washington Dulles, and Dallas/Fort Worth. Sampling ran from October 2023 through August 2024, with Dallas/Fort Worth joining in February 2024.
Does this mean airports are risky right now? No. The data were collected in 2023 and 2024, measure genetic material rather than infectious virus, and do not describe current airport conditions.
Can the samplers identify sick passengers? No. They collect pooled air from a mix of travelers, workers and visitors, which the researchers say limits how precisely results can be tied to arriving flights.
How is this different from wastewater testing? Airplane wastewater captures travelers who use onboard lavatories, while air sampling can pick up people breathing or coughing near the sampler. The authors see the two as complementary, and wastewater detected new COVID variants earlier in this study.
What should travelers do? Stay home or wear a mask when sick, and consider testing before visiting vulnerable relatives. Checking CDC respiratory and wastewater data before a trip gives a picture of local conditions.
