Jet and warm air hand dryers contaminate air in washrooms, study finds

Bacteria are blown into the air, onto users and onto bystanders, risking cross contamination between washroom users

Scientists have found that jet-air and warm hand dryers can spread bacteria in public toilets. A recent study has shown that jet and warm air hand dryers spread bacteria into the air and onto users and those nearby. The findings have significant implications for cleaning, facility and hospitality managers responsible for equipping washrooms in public places.

The study, designed by medical microbiologist Professor Mark Wilcox of the University of Leeds and Leeds Teaching Hospitals, and funded by the European Tissue Symposium (ETS), compared different hand drying methods and their potential to spread bacteria from hands into the air. Jet air dryers were found to spread greater numbers of bacteria-carrying water droplets and to spread them further than other drying methods. In addition, the bacteria still continue to be present in the air for a considerable time after the dryer has stopped.

The study, published in the Journal of Hospital Infection, will be presented to a global audience of professionals, including expert epidemiologists, microbiologists, public health practitioners and directors of infection prevention and control, at this week’s Healthcare Infection Society International Conference in Lyon, France.

In carrying out the study, the researchers contaminated hands with a harmless type of bacteria called Lactobacillus, which is not normally found in washrooms. This was done to mimic hands that have been poorly washed. Subsequent detection of the Lactobacillus in the air proved that it must have come from the hands during drying. The experts collected air samples around the dryers and also at distances of one and two metres away.

Air bacterial counts close to jet air dryers were found to be 4.5 times higher than around warm air dryers and 27 times higher compared with using paper towels. Next to the dryers, bacteria persisted in the air well beyond the 15sec hand-drying time, with approximately half (48%) of the Lactobacilli collected more than five minutes after drying ceased. Lactobacilli were still detected in the air 15min after hand drying.

‘It is not acceptable to have contaminated air in washrooms,’ said Marc Van Ranst, professor in virology and chairman of the Department of Microbiology and Immunology at the University of Leuven in Belgium.

‘Cleaning and facilities managers and those running sporting or catering establishments need to have access to the very latest advice on minimising the spread of infection in washrooms and public places, and to act on it.’

Containment of infection in public places and particularly in washrooms, is also a priority for governments and public health experts.

The extent to which jet-air and warm air dryers dispel microbes in the washroom environment raises questions concerning policy guidance to avoid the spread of infection in hospitals and other public environments. This research shows that hand drying with single use towels has the least risk of airborne microbial contamination.

‘We increasingly emphasise the need to wash hands to control the spread of infection, but we have not considered the best way to dry them,’ said Professor Wilcox.

‘Best does not solely mean convenience. Drying hands using electric dryers risks spreading microbes in the washroom, and this is clearly not desirable when trying to limit the spread of bacteria or viruses from person to person.’

Roberto Berardi of the European Tissue Symposium (ETS) which commissioned the study said: ‘The importance of hand washing to prevent spread of infection is widely accepted. However, to date hand drying has received much less attention.

‘Correct hand drying completes the hand washing process and reduces the risk of microbe transmission. Hand drying alternatives in public washrooms are based on either water absorption (single use paper and textile towels) or water dispersal (warm air dryers, high speed air dryers). This research adds to the existing body of evidence demonstrating that hand drying using towels is associated with lower numbers of microbes both on the hands and in the washroom environment than with warm air or jet air dryers.’