The Air on Planes and in Hospitals Is Cleaner Than You Think — Mostly Skin Microbes, Not Pathogens

The Air on Planes and in Hospitals Is Largely Harmless — But Antibiotic Resistance Shows Up

After the COVID-19 pandemic, many people worry that crowded indoor spaces such as hospital waiting rooms and airplane cabins are full of dangerous airborne pathogens. New research published in the journal Microbiome offers some reassurance: the airborne microbial communities sampled from hospitals and airplanes were diverse and largely composed of benign skin microbes, not active disease agents.

What the Study Found

A team led by researchers at Northwestern University (with collaborators at the Harvard T.H. Chan School of Public Health and Argonne National Laboratory) detected 407 distinct microbial taxa by analyzing DNA recovered from the outer surfaces of 22 used disposable face masks. Most taxa were common human skin commensals such as Staphylococcus epidermidis and Cutibacterium acnes. Potential pathogens like Escherichia coli appeared at low densities and did not indicate active infections among occupants.

“Indoor air looks like indoor air, which also looks like human skin,” said Erica Hartmann, a synthetic biologist at Northwestern and a co-author of the paper. Humans normally carry roughly 10^12 microorganisms on their skin and continuously shed millions of skin cells, which helps explain this pattern.

Antibiotic-Resistance Genes: A Notable Concern

Although most microbes detected were harmless skin bacteria, the researchers also identified 23 different antibiotic-resistance genes across samples — associated with major antibiotic classes including gentamicin and streptomycin. The presence of these genes does not mean active drug-resistant infections were present in the sampled environments, but it does highlight a broader public-health issue: resistance genes circulate in shared indoor spaces and deserve monitoring.

Method: Masks as Passive Air Samplers

Sampling airborne microbes is technically challenging because air is constantly moving and microbes are tiny. To address this, the team repurposed used disposable face masks as inexpensive, passive collectors of airborne material. Travelers wore masks during domestic and international flights, and hospital staff wore masks during shifts; participants then sealed the masks in sterile bags and mailed them to the laboratory. Unworn masks served as negative controls. The researchers applied a shotgun metagenomics approach to extract and sequence DNA from the masks' outer surfaces.

Limitations and Context

The mask-based approach is a clever, low-cost way to estimate personal and environmental exposures, but the study has limitations: the sample size was small (22 masks), and masks capture a combination of exhaled, deposited, and ambient microbes rather than providing an absolute airborne concentration at a given moment. Despite those caveats, the findings are consistent with other work showing that indoor air microbiomes often reflect the people who occupy the space.

Implications

For most people, the study offers reassurance that the microbes floating in crowded indoor air are commonly harmless skin residents rather than rampant pathogens. Still, the detection of multiple antibiotic-resistance genes in both hospitals and airplanes suggests that surveillance of resistance markers in built environments could be valuable for public health. Simple tools like used face masks may help expand monitoring at scale.

Lead image: Zubada / Shutterstock
Originally reported by: Nautilus