If you’re looking to avoid getting sick, chances are you’ll steer clear from visiting a hospital or traveling by plane—environments packed with people and their germs. A new study, however, demonstrates that hospital and airplane air are cleaner than we typically imagine.
Researchers analyzed an aircraft air filter, along with face masks worn by travelers and healthcare workers, to investigate the air in airplanes and hospitals. A study published today in the journal Microbiome reveals that the air in both environments primarily hosts harmless microbes usually related to human skin.
“We realized that we could use face masks as a cheap, easy air-sampling device for personal exposures and general exposures,” Erica Hartmann, lead author of the study and an environmental microbiologist at Northwestern University, said in an emailed university statement. “We extracted DNA from those masks and examined the types of bacteria found there. Somewhat unsurprisingly, the bacteria were the types that we would typically associate with indoor air. Indoor air looks like indoor air, which also looks like human skin.”
Used face masks
Overall, Hartmann and her colleagues identified 407 microbial species, such as ordinary skin bacteria and environmental microbes. They also found very few possibly disease-causing microbes without evidence of active infection. Unsurprisingly, the idea for the study dates back to January 2022, at the heart of the covid pandemic. Hartmann received a grant to search for pathogens in airplanes’ cabin filters but realized that investigating high-efficiency particulate air (HEPA) filters might be complicated.
“At the time, there was a serious concern about Covid transmission on planes,” explained Hartmann, an expert on indoor microbiomes. Because HEPA filters are very efficient, “we thought it would be a great way to capture everything in the air. But these filters are not like the filters in our cars or homes.” They are very expensive, and “in order to remove them, workers have to pull the airplane out of service for maintenance. This obviously costs an incredible amount of money, and that was eye opening.”
Indoor air looks like indoor air, which also looks like human skin.
That was when the team thought of a much cheaper and simpler tool that also captures microbes passively: face masks. As such, the team collected face masks from volunteers who wore them on domestic and international flights. The volunteers also sent face masks that accompanied them on flights but were never worn, for comparison. To investigate the difference between indoor environments, the researchers chose another busy, closed space with heavily filtered air: hospitals. And so they gathered face masks from hospital workers after they’d worn them during a work shift.
Microbe DNA
The researchers analyzed DNA from the exterior of each mask, finding that the air in both environments contains a diverse but mostly harmless blend of microbes, with little evidence of any that might be pathogenic. The samples from both spaces mostly consisted of common bacteria associated with humans, especially ones in indoor air and from our skin. What’s more, the microbes from both environments were very similar, though the amount of each microbe differed slightly. Ultimately, the similarities indicate that microbes in both airplane and hospital air come from the people themselves—notably, their skin, not their sickness—and not the particular environment.
The researchers also found some antibiotic resistance genes associated with major categories of antibiotics. This doesn’t mean there are dangerous microbes floating around, but it does point out the extent to which antibiotic resistance has spread.
Furthermore, “for this study, we solely looked at what’s in the air,” Hartmann concluded. “Hand hygiene remains an effective way to prevent diseases transmission from surfaces. We were interested in what people are exposed to via air, even if they are washing their hands.”
The study should come as good news to everyone looking to fly during the upcoming holidays.
