Just in time for the busy holiday travel season, researchers report on a question that will run through many people’s minds as they cram into tightly packed planes: How clean is airplane air?
To find out, Erica Hartmann, associate professor in the department of civil and environmental engineering at Northwestern University, and her colleagues tested face masks worn by passengers on flights to log what kinds of bugs these products trapped. The team was also interested in the air circulating in hospitals, another public place where germs commonly spread, and tested face masks worn by hospital personnel.
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The team collected 53 masks in sterile bags and cut out the outer layers to analyze just the microbes circulating in the air and not in people’s respiratory passages, then extracted and analyzed DNA from them. To ensure they were detecting all the microbial DNA present, they also used an amplification process called PCR to enrich what was present on the masks.
Overall, they report in the journal Microbiome, they detected 407 microbial species from both the plane and hospital settings, with similar populations of bugs from each. The vast majority of these came from skin and are harmless, says Hartmann. “This is not surprising, because a lot of the microbes in buildings and in the air around us reflect us,” she says. “A lot of the surfaces we touch tend to have skin-associated bugs because we are transferring bugs every time we touch something. We shed microbes everywhere we go—I and my colleagues refer to it as a microbial aura.”
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The kits that the team used to extract the genetic material from the microbes were designed to collect DNA, so that meant the researchers captured primarily bacteria—not viruses, many of which have RNA as their genetic base (such as COVID-19 and influenza). While people might be more concerned about how much virus is floating around a confined space like an aircraft cabin, Hartmann says that viruses are likely to make up a smaller proportion of microbes in the air than bacteria, since people are shedding bacteria from the skin in larger amounts than they are releasing virus particles.
She notes that viruses tend to be very dependent on the right habitat in order to thrive, and once outside the body and away from cells that they can infect, they can become slightly less virulent—although there are plenty of examples of viruses surviving on surfaces, and studies show that it only takes a small amount of virus to infect someone and make them sick.
The results of the study highlight the importance of developing better ways to monitor the air for disease-causing pathogens, including viruses, using filtration and sensing systems that could provide more real-time readings. “Imagine something like a carbon monoxide sense or a gas alarm, that, depending on the levels of microbes present, could automatically increase air exchange rates or alert people to put on masks,” says Hartmann. “Factoring in health and having the capability 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 happen indoors, the air—even in tight places like a plane or hospital—may not be as full of disease-causing germs as we think. The other lesson: face masks are an effective way to protect yourself from pathogens that might be circulating in the air (as well as protecting you from spreading germs to others if you are sick).