A new study has found that the air circulating in high-traffic public spaces, such as aeroplanes and hospitals, contains mostly harmless microbes commonly found on human skin.
The Northwestern University in Illinois describe their research as the first study of its kind, in which they turned to unconventional sampling methods – used face masks and an aircraft air filter.
By extracting DNA from these materials, the team uncovered the microbial ‘fingerprint’ of shared indoor air and discovered that aeroplane and hospital environments host remarkably similar microbial communities.
Across all samples, researchers identified 407 microbial species, primarily skin-associated bacteria and environmental microbes. Only a small fraction of potentially pathogenic species appeared and even then in extremely low abundance and without indicators of active infection.
Northwestern’s Erica M. Hartmann, who led the study. said: ‘We realised that we could use face masks as a cheap, easy air-sampling device for personal exposures and general exposures. 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.’
The project originated during the COVID-19 pandemic in January 2022, when public concern about the safety of airplane cabin air was at a peak. With support from the Walder Foundation, Hartmann initially set out to analyse a HEPA filter from an airplane—one that had been in service for more than 8,000 flight hours. But she quickly encountered a major obstacle.
‘At the time, there was a serious concern about Covid transmission on planes,’ Hartmann said. ‘HEPA filters on planes filter the air with incredibly high efficiency, so 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 cost thousands of dollars 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.’
The team thus turned to face masks as an inexpensive alternative. Volunteers wore masks on domestic and international flights, then mailed them to Hartmann’s lab. Additional masks worn by hospital workers served as a comparison, along with control masks that volunteers carried on flights but never wore.
Hartmann explained: ‘As a comparison group, we thought about another population of people who were likely wearing masks anyway. We landed on health care providers.’
DNA extracted from the mask exteriors revealed that hospitals and aeroplanes share highly similar microbial profiles. Human-associated bacteria – especially those originating from skin – dominated both environments, indicating that people themselves are the primary source of airborne microbes. The team also detected several antibiotic resistance genes, underscoring their prevalence in the broader environment.
However, Hartmann cautions that airborne microbes are only one element of disease transmission. ‘For this study, we solely looked at what’s in the air. 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 full research can be read here.
Photo: Karsten Winegeart / Unsplash
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