I edited a paper for Journal of Hospital Infection a few years ago on the potential risk of warm air dryers and especially jet air dryers compared with paper towels in spreading microbial contamination via the air. The paper showed that hands dipped in a concentrated bacterial suspension resulted in fairly widespread bacterial contamination of the air; jet air dryers were the worst culprit, followed by warm air dryers, with paper towels resulting in markedly less contamination. They also did some cool paint splatter experiments to visualize potential contamination routes (see image above, from the paper).
This study got a fair bit of press coverage, and perhaps unsurprisingly sparked a bit of manufacturer “tit for tat” criticism of the study, much of which was valid to a lesser or greater degree (see this Guardian article on Dyson and Kimberly Clark in “hand to hand combat” (ha ha) on this issue).
And so to today’s article for consideration. A comparison of viral air contamination associated with paper towels (PT) v warm air dryers (WAD) v jet air dryers (JAD). Hands were artificially contaminated with a bacteriophage (MS2), which is is often used as a surrogate for contamination with pathogenic viruses. The hands were then dried using one of the three methods (without an actual washing step). Several different dispersal tests were performed: contamination at various heights 0.4m from the drying point, level of contamination at various distances from the drying point, and contamination at a fixed point over a 15 minute period. Air sampling was employed in addition to “settle plates”. By all measures, the JAD resulted in most contamination, which was markedly greater than either the WAD and PT. WAD also resulted in more contamination than PT, but the difference was not as great.
The major criticism of the study is that the concentration of the bacteriophage was extremely high (1010 pfu per mL), and 50mL was applied leading to a whopping dose of 1011 pfu applied to the hands. Furthermore, hands were not actually washed prior to the drying tests – only ‘simulated washing’ was performed. Thus, this is worst case scenario in extremis.
There’s another important point too, which relates to behavior and patience. From my own experience of hand dryers, I rarely have the patience to stand there long enough to let my hands actually dry so usually end up deploying the back of the trouser wipe. Whilst this isn’t necessarily a microbiological risk (I have very clean trousers), it often leaves me with damp hands, which is bad news for hand hygiene. This problem is likely to be less acute for JADs than for WADs – but a problem with them both nonetheless.
So what are the implications for infection prevention and control? Although this study highlights theoretical risk rather than actual risk (because we don’t know how representative these experiments are in modeling the real risk on the wards), there is enough here for me to side with paper towels and no hand dryers in clinical areas.
Reflections on Infection Prevention and Control 
Thanks Jon,
‘Hand driers versus paper towels’ is certainly a polemic topic, with each side accusing the other of bias.
What do you think of contamination of paper towel dispensers (and undispensed paper towels) due to contact from improperly-washed hands?
Do you see an case for making (at least parts of) paper towel dispensers from Antimicrobial Copper alloys?
Also the touch-parts of hand driers…
Welcome your thoughts.
Andrew Cross
ACT Surfaces Ltd
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Yes certainly some logic in making hand hygiene equipment antimicrobial somehow.
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Jon, we were trying to tell a Facilities Management Co. that their newly installed hand-driers were likely contributing to an unhealthy merry-go-round of the clients washroom germ levels but their immediate answer was; ‘ours have filters which stop that happening’. – http://www.dyson.co.uk/hand-dryers/hygiene.aspx – If I judge correctly; however clean the air is that exhausts to dry your hands, if those hands are still partially dirty then those germs promptly, in part, becomes airborne and come to rest on washroom surfaces. Unhealthy & infection-productive biofilm then occurs unless surface sanitization is of a suitable quality each day?
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Precisely. Clean air blown onto contaminated hands = risk of spreading contamination.
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Jon – you nailed it again. Can I re-post this in the LinkedIn Hospital Infection Control group?
I would also suggest paper towels for this reason – consistently the most contaminated surfaces we have found in hospitals (as tested with ATP tools) have been the INSIDE door handle of staff washrooms. That warrants a whole other discussion.
But when the issue is properly highlighted to staff, qualitative feedback has been that staff switch to using paper towels when opening the bathroom door.
That said – we believe the majority of staff do NOT wash their hands after going to the bathroom and we have some evidence to support this. However, anonymous surveillance of staff in the bathroom is not consistent with good staff engagement strategies – so data on this is limited. But there is a grant-study here…
– Niall Wallace
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Yes post away! But important to note this issue should not be seen in the context of washroom hygiene only. Hand hygiene is most important during and after direct patient contact. This is the point at which I would be most concerned about air / jet dryers spreading contamination.
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I’d be interested to hear from any hospitals who have decided to introduce air or jet hand dryers into clinical areas?
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I feel ambivalent about this – because if hands have been properly washed, the transient contamination which you are trying to remove should no longer be present on the hands at levels likely to cause infection i.e they should be “fit for purpose” – so whats the worry? I guess its about minimising risk – is the residual risk sufficient to warrant action. If it is then I would like to see which is the more risky – dispersal of residual microbes on hands after HW through the air by use of dryers or dispersal to surfaces through hands which are still damp
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When air passes over a heat exchange surface, which is what is happening in air hand driers, the air put out is affected by the cleanliness of the unit. This is in part the reason why HVAC condenser and evaporator coils are cleaned; if they are dirty then the air that passes over / through them is likely to be contaminated in the process.
Most air hand driers are in bathrooms / restrooms, which usually have a higher relative humidity level than most other areas in say an office or healthcare facility. As such the potential for biofilm to form on the inside of an air hand dryer is high, just as it is with the condenser and evaporator coils in HVAC air handling units (AHUs).
Biofilm on coils in HVAC systems is the major impediment to the thermal transfer efficiency of those heat exchange systems, and is also where the pathogen count is usually highest in an air system.
So these air hand driers are usually contaminated with biofilm (filters will not prevent this) and they are virtually never cleaned, so its no wonder they are throwing off so much “dirt”.
To Anderw Cross’s point, antimicrobial coatings are going to be minimally impactful, just as they have proven to be minimally impactful in HVAC systems.
To Andrew Robertson’s point that the FMs are claiming that their units have air filters on them, that may work well for a matter of days / weeks depending on the usage rates, but how often do they replace those filters and what is the MERV rating of them? Also, as I noted earlier, the humidity level in the areas of a facility where such units are operating is higher, and no amount of filters, nor how regularly they are replaced, will prevent the resultant build up of biofilm on the inside of these units.
To Sally Bloomfield’s point, given the concentration of the air that has passed over the dirty internal workings of the air hand driers relative to the surface of the hands receiving it, assuming a duration of say 10 to 15 seconds exposure, then this is not a subject to be ambivalent about. The hands when put under the air from these machines are wet, and you are blowing volumes of contaminated air over them. Biofilms are formed by dripping water onto a surface and allowing the planktonic bacteria to attach, start to colonize and so form a biofilm. When wet hands are placed under these devices and subjected to volumes of air carrying pathogen bacteria, no matter how clean the hands are from the washing process, they are now contaminated.
Probiotic cleaners have been used to remove the biofilm from HVAC coils and other components in and AHU, and could also be used on these devices, but I see little to no chance of already constrained maintenance and cleaning resources in facilities being diverted to address this issue. In essence I believe they should be discontinued.
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Thank you for the information, Jon Otter
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