A new study in Applied and Environmental Microbiology (Sci-Hub mirror) conducted microbial surveys of the bathrooms at the University of Connecticut (where the study's lead authors are based) to investigate whether hand-dryers were sucking in potentially infectious microbes and then spraying them all over everything, as had been observed in earlier studies.



They were.

The full cycle goes like this: when you flush a toilet that doesn't have a lid, the turbulence of the flush sends fecal particles into the air, where they hover in a miasmic cloud; when the dryers switch on, they pull these particles in through their intake, heat them up, and spray them onto your moist hands and other moist, hospitable surfaces where their bacteria can thrive.

HEPA filters greatly reduce this mechanism.

The new study specifically focuses on lower-powered hand-dryers, which some people had believed were less prone to sucking in tiny pieces of shit and spraying them on you.

Earlier studies on hand-dryers were tainted by funding from companies that manufactured paper towels, but as far as I can tell, no such conflict exists here.



PS533 "was almost certainly dispersed throughout bathrooms in the research areas as spores, which would easily survive desiccation in room air, as well as the elevated temperatures in hand dryer air; however, growing or stationary-phase bacteria would not be nearly so hardy as spores," the authors note. "However, the facile dispersion of one bacterial strain throughout a research facility should probably be a concern to risk assessors and risk managers when dispersion of potentially pathogenic bacteria is considered." In a final test, the researchers did a cursory look at some of the other bacteria the dryers were blowing around. They found that with or without a HEPA filter, the blowers stirred up potential pathogens, including Staphylococcus aureus.



The findings should be a wake-up call to managers of research and clinical settings. The authors note that Clostridium difficile—a devastating and intractable diarrheal plague—also forms spores, and researchers have found that a flushing toilet can easily launch it into the air.



"This suggests another means of C. difficile transmission and one that may not be interrupted by either hand washing or traditional surface decontamination methods," the authors conclude. "The role of this potential mode of C. difficile transmission is worthy of future study."

Deposition of Bacteria and Bacterial Spores by Bathroom Hot-Air Hand Dryers [Luz del Carmen Huesca-Espitia, Jaber Aslanzadeh, Richard Feinn, Gabrielle Joseph, Thomas S. Murray and Peter Setlow/Applied and Environmental Microbiology] (Sci-Hub Mirror)

Hot-air dryers suck in nasty bathroom bacteria and shoot them at your hands [Beth Mole/Ars Technica]

(Image: Rusty Clark, CC-BY)