What's safer — the air in a plane or in a hospital? Germophobes may breathe a little easier after learning the findings of a study by researchers from Northwestern and Harvard Universities.

The team tested the air quality in airplanes and hospitals for microbial DNA. They gathered samples from an airplane's high-efficiency particulate air (HEPA) filter and from the outsides of face masks worn by passengers. They also tested masks taken on flights but never worn.

If researchers can monitor what microbes are in the air, public health authorities can decide if and how to prevent the spread of infectious diseases.

In the hospital, the researchers tested the masks worn by healthcare workers.

Some airborne microbes can cause disease, but many are totally harmless. Across all the over 400 DNA samples they tested, the researchers found mostly harmless species of microbes.

Airborne samples are already less likely to spread disease. Being in direct contact with an infected person or a surface touched by many people is more likely to spread disease, Erica Hartmann, lead author on the study, told TheDoctor in an email.

You might be surprised to learn that the microbes in the air inside planes and in hospitals were very similar. The overlap of these microbial populations suggests that most of the airborne microbes in both locations come from humans. The most common microbes in each place were bacteria found on human skin.

Very low quantities of potentially disease-causing microbes were found, however, and the researchers also reported a few genes for antibiotic resistance which they identified as more evidence that antibiotic resistance has become widespread.

This was a proof-of-concept study. Its goal was to see if face masks could be used to sample air in certain environments. “The use of face masks as convenient air samplers could be really helpful for public health monitoring,” Hartmann said.

Most of the airborne microbes in hospitals and airplanes come from humans.

The idea was that if researchers can monitor what microbes are in the air, public health authorities can decide if and how to prevent the spread of infectious diseases. The study is one step toward developing the technology needed to detect microbes of interest and determine if they cause disease, Hartmann, an associate professor of civil and environmental engineering at Northwestern, explained.

“It would be amazing to have something like a carbon monoxide detector that acts as a real-time sensor that tells us when to increase air flow in a certain area or ask people to wear a mask,” she added.

The study is published in Microbiome.