Just in time for the busy holiday travel season, researchers report a question that will be on the minds of many people crammed into tightly packed planes: How clean is the air on planes?
To find out, Erica Hartmann, an assistant professor of civil and environmental engineering at Northwestern University, and her colleagues tested face masks worn by passengers on flights to determine what types of errors the products caught. The team also looked at the air circulating in hospitals, another public place where germs commonly spread, and tested face masks worn by hospital staff.
The team collected 53 masks in sterile bags and cut out the outer layers to analyze only germs circulating in the air, not in people's respiratory tracts, and then extracted and analyzed DNA from them. To make sure they were detecting all the microbial DNA present, they also used an amplification process called PCR to enrich for what was present on the masks.
Overall, they report in the log MicrobiomeThey found 407 species of microbes in both the airplane and the hospital, with similar insect populations in each. The vast majority of them occur through the skin and are harmless, Hartmann said. “This is not surprising because many of the microbes in the buildings and air around us reflect us,” she says. “Many of the surfaces we touch tend to have skin-associated germs because we transmit germs every time we touch something. We spread germs everywhere we go—my colleagues and I call this a germ aura.”
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The kits the team used to extract genetic material from microbes were designed to collect DNA, so the researchers captured mostly bacteria rather than viruses, many of which have RNA as their genetic basis (like COVID-19 and influenza). While people may be more concerned about the number of viruses floating around in a confined space like an airplane cabin, Hartmann says viruses likely make up a smaller proportion of airborne microbes than bacteria because people shed bacteria from their skin in larger quantities than they shed virus particles.
She notes that viruses tend to be very dependent on a suitable environment to thrive, and once outside the body and away from the cells they can infect, they may become slightly less virulent.
The study's findings highlight the importance of developing better ways to monitor air for disease-causing pathogens, including viruses, using filtration systems and sensors that could provide more real-time readings. “Imagine something like a carbon monoxide detector or gas alarm that, depending on the level of microbial presence, could automatically increase air exchange rates or alert people to wear masks,” Hartmann says. “Taking health into account and being able to make informed decisions about how to protect yourself would be amazing.”
Until then, Hartmann hopes people will remember that as the weather gets colder and more gatherings take place indoors, the air—even in tight spaces like an airplane or a hospital—may not be as full of pathogens as we think. Another lesson: Face masks are an effective way to protect yourself from pathogens that may be floating in the air (and also protect you from spreading germs to others if you're sick).
