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.