The air present indoors in passenger cabins and in the aisles is poor in pathogens and is instead teeming with microorganisms that live on our skin.
The most feared indoor air in the Covid era, that of airplane cockpits and hospital interiors, is not crowded with pathogens, but populated by the same harmless bacteria present on human skin.
This was established by research published in the magazine Microbiome who used an unsuspected tool for indoor air sampling: masks, which in their external part captured bacteria and other invisible microorganisms present in crowded places full of human interactions, such as airplane cabins and hospital corridors.
Masks to analyze
A group of environmental and civil engineers from Northwestern University (United States) planned to investigate the composition of indoor air in airplanes and hospitals in 2022, during the second phase of the pandemic, when those who had resumed traveling were worried about the risk of in-flight infections. The initial idea was to analyze HEPA (High-Efficiency Particulate Air) filters, high-efficiency filtration systems that entirely change the air in the aircraft cabin every two or three minutes. But these filters are very expensive and difficult to dismantle: removing them for analysis would not have been sustainable.
Hence the idea of using masks as “passive” traps. From the analysis of the DNA left on the outside of those worn on national or international flights, and placed in sterile bags as soon as the passengers disembarked, scientists traced the bacteriological composition of the air breathed on those planes. At this point, they compared the microorganisms present in the air inside the planes with those linked to the DNA captured from the masks of hospital workers during a work shift.
Few bad bacteria and many skin hosts
In both contexts, a varied community of almost always harmless microorganisms was found, with minimal traces of pathogens, where the bacteria most often associated with our species, such as those that live on human skin, dominated. The overall composition of the microbial communities found in the two different environments was also very similar, precisely because it can be traced back to the simple human presence and not to specific diseases. What changed instead was the abundance of the individual microorganisms found.
A now common phenomenon
Among the genetic traces remaining on the masks, the genes of antibiotic resistance developed towards one of the main classes of antibiotics were also found. It does not mean – the authors point out – that there were bacteria resistant to antibiotics in the air, but rather that antibiotic resistance genes are now more widespread than we think.
