Deposition of Bacteria and Bacterial Spores by Bathroom Hot-Air Hand Dryers

Hot-air hand dryers in multiple men's and women's bathrooms in three basic science research areas in an academic health center were screened for their deposition on plates of (i) total bacteria, some of which were identified, and (ii) a kanamycin-resistant Bacillus subtilis strain, PS533, spores of which are produced in large amounts in one basic science research laboratory. Plates exposed to hand dryer air for 30 s averaged 18 to 60 colonies/plate; but interior hand dryer nozzle surfaces had minimal bacterial levels, plates exposed to bathroom air for 2 min with hand dryers off averaged ≤1 colony, and plates exposed to bathroom air moved by a small fan for 20 min had averages of 15 and 12 colonies/plate in two buildings tested. Retrofitting hand dryers with HEPA filters reduced bacterial deposition by hand dryers ∼4-fold, and potential human pathogens were recovered from plates exposed to hand dryer air whether or not a HEPA filter was present and from bathroom air moved by a small fan. Spore-forming colonies, identified as B. subtilis PS533, averaged ∼2.5 to 5% of bacteria deposited by hand dryers throughout the basic research areas examined regardless of distance from the spore-forming laboratory, and these were almost certainly deposited as spores. Comparable results were obtained when bathroom air was sampled for spores. These results indicate that many kinds of bacteria, including potential pathogens and spores, can be deposited on hands exposed to bathroom hand dryers and that spores could be dispersed throughout buildings and deposited on hands by hand dryers.IMPORTANCE While there is evidence that bathroom hand dryers can disperse bacteria from hands or deposit bacteria on surfaces, including recently washed hands, there is less information on (i) the organisms dispersed by hand dryers, (ii) whether hand dryers provide a reservoir of bacteria or simply blow large amounts of bacterially contaminated air, and (iii) whether bacterial spores are deposited on surfaces by hand dryers. Consequently, this study has implications for the control of opportunistic bacterial pathogens and spores in public environments including health care settings. Within a large building, potentially pathogenic bacteria, including bacterial spores, may travel between rooms, and subsequent bacterial/spore deposition by hand dryers is a possible mechanism for spread of infectious bacteria, including spores of potential pathogens if present.