Comparative evaluation of the hygienic efficacy of an ultra-rapid hand dryer vs conventional warm air hand dryers

A study published in the Journal of Applied Microbiology (1) was done to compare an ultra-rapid hand dryer against warm air dryers, with regard to: (A) bacterial transfer after drying and (B) the impact on bacterial numbers of rubbing hands during dryer use.
With most hand washing regimens, the numbers of bacteria on the skin surface are lowered, but not eliminated. If hands are not then dried properly, transfer of commensal strains, or transients not eliminated by the wash itself, is more likely to occur. The degree of wetness of hands appears to greatly influence bacterial transfer and dissemination to surfaces and items touched. This probably occurs not only because of the physical aspects of moisture droplets transferring between one surface and another but also because the bacteria may be maintained in a physiological state that makes them better able to survive in the new environment. It is mentioned that by drying the hands, the numbers of bacteria transferred to samples of skin, food or utilities were reduced by an order of 99%.
The four main methods of hand drying are letting the skin dry by evaporation, use of paper towels, cloth towels, or, in more recent times, use of warm air dryers
In this study, fourteen volunteers (seven men and seven women), above the age of 18 years were recruited to take part in the study. The volunteers handled raw chicken, and after a standard handwash and use of one of the different dryers, the transfer of residual bacteria from the fingertips to foil was quantified. Two models of air-dryer and a new Airblade dryer (This is an ultra-rapid dryer that uses two high-pressure ‘knives’ of HEPA-filtered air (at ambient temperature) to strip water from hands that are held apart as they are drawn upwards through the airstream) was used.
It was seen that when a standard drying time of 10 s was applied, the Airblade™ unit performed considerably better (i.e. resulted in less residual bacterial transfer) than all the other methods of drying, with all the results being strongly statistically significant (i.e. P < 0•050). When the manufacturer’s preset device activation times were used with the Turbodry™ and A5 machines, their performance greatly improved (P < 0•050), but was still less than that observed with the Airblade™ unit after just 10 s. For the drying time of 10 s, both the Turbodry™ and A5 machines were associated with higher mean levels of bacterial transfer than when using no dryer at all, but the results were not statistically significant (P > 0•050).
The other parameter studied was the effect of rubbing of hands during drying. In many instances, the bacterial numbers transferred from hands actually increased because of the rubbing action. The results obtained from the rubbing experiments were, in most cases, statistically significantly different from those obtained when holding hands still under the same devices (P < 0•050). When keeping the hands still, there was no statistical difference between any of the dryers, for any anatomical site, and the bacterial reduction in the middle of the fingers was comparable to that obtained with paper towel drying. Rubbing the hands with paper towels proved to be very effective at removing bacteria from the hands, with results that were in most cases statistically significant (P < 0•050). In particular, rubbing with paper towels appeared to be the best means of reducing bacterial loading on the fingertips.
When hands were held stationary (palm up) in the air stream under these units, the reduction in counts of bacteria subsequently transferred from the skin was much greater than when the hands were rubbed together. Indeed, for some sites, the bacterial count increased markedly when hands were rubbed.
The study conclusively demonstrates that effective hand drying is important in preventing the postwash translocation of bacteria from the surface of hands to the next surfaces touched. The results provide an evidence base for the development and enhancement of hygienic hand drying practices. The authors have also concluded that the ultra-rapid Airblade™ hand dryer is superior to the warm air dryers for reducing bacterial transfer. The lack of paper waste, coupled with its short, 10 s drying time and use of HEPA-filtered air should encourage greater compliance with hand drying and thus help reduce the spread of infectious agents by the hand-borne route.
(1)A.M. Snelling, T. Saville, D. Stevens, C.B. Beggs. Comparative evaluation of the hygienic efficacy of an ultra-rapid hand dryer vs conventional warm air hand dryers. Journal of Applied Microbiology. Published onlin 7,September,2010.
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2010.04838.x/full