A CDC-led surveillance project that pulled air through samplers near international arrivals at four major U.S. airports detected genetic material from the virus that causes COVID-19 in 98.3% of samples, according to a study published Sept. 9 in PLOS Global Public Health. Influenza A turned up in 17.2% of samples.
The airports were San Francisco International, Newark Liberty International, Washington Dulles International, and Dallas/Fort Worth International, major gateways for the Bay Area, the New York and New Jersey region, Washington, D.C., and North Texas. For anyone flying this fall, the headline number can sound like a warning, but it is not a measure of the chance that any traveler will get sick.
The samplers were designed to reveal which viruses are circulating in a crowd, not to estimate who is contagious or how much virus a person breathes in. The study measured viral genetic material rather than live virus, and it did not track whether anyone near the samplers became infected.
Four Gateways, 10 Months of Filtered Air
CDC ran the project with Ginkgo Biosecurity and the University of Wisconsin-Madison. From Oct. 18, 2023, to Aug. 27, 2024, samplers sat on tables 28 to 30 inches off the floor in congregate areas beside customs and immigration inspection, near several hundred arriving international passengers. Sampling at Dallas/Fort Worth ran from February to August 2024, and each unit collected air for 10 hours a day, the study reported.
The team collected 463 samples, and 460 passed a quality check. Of those, 452 tested positive for SARS-CoV-2, the virus that causes COVID-19. Positivity was 97.9% in San Francisco, 98.4% at Newark, 97.5% at Dulles, and 100% at Dallas/Fort Worth. 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.
Flu detections showed up weekly from Jan. 1 to March 18, 2024, appeared sporadically through April 22, and then stopped. Sequencing identified 30 viral species, including RSV and seasonal coronaviruses. COVID lineages in the air, including JN.1 and later KP.2 and KP.3, matched those found in aviation wastewater at the same airports, CIDRAP reported.
Flu Tracked the Season While COVID Signals Did Not
The comparisons with other data sources make the findings more nuanced. At San Francisco and Dulles, the two airports with overlapping data, influenza levels in the air lined up with aviation wastewater, nasal swabs volunteered by arriving travelers, and national clinical testing. COVID measurements in the air did not significantly track any of those sources.
The authors offer a likely reason. Flu circulated seasonally at lower background levels, while COVID was detected almost constantly, so a simple positive result told investigators little. That makes genetic sequencing the more useful tool for tracking new COVID variants. Aviation wastewater also detected KP.2 and KP.3 about six weeks earlier than the air samples did.
The authors concluded that air sampling can complement aviation wastewater surveillance, although "performance and concordance vary by pathogen and sample type." They wrote that air monitoring could eventually inform ventilation, air purification, and public health messaging at ports of entry. The project adds to CDC's Traveler-based Genomic Surveillance program, which already collects nasal swabs and aircraft wastewater.
MedicalDaily recently reported on a separate study that found RSV genetic material in air near hospitalized patients. Together, the studies show air sampling spreading into new settings, while its value for individual risk decisions remains unproven.
Detection in the Air Is Not the Same as Infection Risk
This was a surveillance feasibility study, not a risk study. It used PCR testing, did not grow live virus, and did not follow travelers. Terminal air also reflects a mixed population of airport workers, domestic travelers, and visitors, so the authors note it cannot be tied cleanly to inbound international flights. Detection limits and ideal sampler placement still need study.
The paper's disclosures matter for readers weighing the findings. The work was conducted as a CDC surveillance activity, and some academic work was also supported by private donors and state and federal grants. Seven authors were employed by Ginkgo Bioworks at the time of the study and hold or received equity in the company, and two University of Wisconsin authors are managing partners of a consultancy that advises on environmental monitoring. The data are also about two years old and describe the 2023-24 season.
For individual travelers, real risk depends on what is circulating now, how crowded and ventilated a space is, how long someone spends near others, and personal health. Adults 65 and older, people with weakened immune systems, and people with chronic medical conditions are more likely to develop serious illness from COVID or flu.
COVID activity is shifting. As of Sept. 16, CDC estimated that infections were growing or likely growing in 27 states, declining or likely declining in 13, and not changing in 10, according to its epidemic trends page. Flu trend estimates for the 2026-27 season had not yet begun.
Reasonable steps for fall travel are familiar ones. Stay current on recommended vaccines, stay home when sick, and consider a well-fitting mask in crowded terminals if you are at higher risk. Test if symptoms start after a trip, and ask a clinician promptly about treatment if you are in a higher-risk group. Changing travel plans based on this study alone is not necessary.
The authors call for more research on airflow, sampler placement, and detection limits before air monitoring is deployed widely. For travelers, the study shows how well scientists can spot viruses in a crowd, not how likely any one person is to catch them.
Key Questions Answered
What did the airport air study find?
Air samplers near international arrivals at four U.S. airports detected SARS-CoV-2 genetic material in 98.3% of valid samples and influenza A in 17.2%, from October 2023 through August 2024.
Which airports took part?
San Francisco International, Newark Liberty International, Washington Dulles International, and Dallas/Fort Worth International.
Does this mean airports are dangerous for travelers?
No. The study detected genetic material, not live virus, and did not measure whether anyone became infected. It cannot estimate an individual traveler's risk.
Why did flu results match other data while COVID results did not?
The authors suggest flu circulated seasonally at lower levels, while COVID was detected nearly all the time, which made simple positive results less informative.
Who funded the study, and are there conflicts of interest?
It was conducted as a CDC surveillance activity, with some academic work supported by other grants and donors. Seven authors worked for Ginkgo Bioworks and held or received equity, and two academic authors are managing partners of an environmental monitoring consultancy.
What should travelers do this fall?
Stay current on recommended vaccines, stay home when sick, consider a mask in crowded spaces if at higher risk, and test if symptoms develop after travel.
