If you wash your hands after using a public washroom and then use a dryer, you may well leave the place with your hands dirtier than before you got in.
Hand dryers installed in public toilets do not just blow air — they also suck it in as well. In doing so, they also siphon bacteria and other microbes carried by passersby, or left in the toilet by those who would not have lowered the lid. After having sucked in these microbes, the dryers reject them again – and in abundance – according to a recent study.
For the purposes of this experiment, researchers at the University of Connecticut’s Faculty of Medicine tested their own public toilets. They discovered that hand dryers created real bacterial highways, invisible in the bathroom air. And these redistributed bacteria did not just land on the occupants of the toilet: thanks to the high energy blowers, they were also scattered throughout the building.
As part of their study, the researchers put 36 glucose-coated plates in the washrooms of their building – with the hand dryers turned on and off – and checked for bacterial plaque growth. When the hand dryers were not turned on, the researchers did not find many bacteria — an average of six colonies per plate. But when the fans were operational, the bacteria were present in abundance, with an average of 60 colonies growing on each plate!
The researchers checked inside the dryers to see if internal microbial buildup could play a role. Although they detected the presence of bacteria when they cleaned the dryers, they were not numerous enough to account for the amount distributed by the dryer airflow.
If the bacteria captured on the plates did not come directly from the hand dryers, they had to come from the air in the bathroom, probably expelled into the air by toilet flushes. Several samples from different bathrooms included the microbe Bacillus subtilis, an occupant of the human gut. But B. subtilis was not alone: the plates exposed to hand dryers contained a total of 62 types of bacteria representing 21 species, including Staphylococcus aureus, a common bacterium that remains associated with serious infections.
One of the measures that could help reduce bacterial circulation in bathrooms would be to install hand dryers with High Efficiency Particulate Air filters, note the researchers. By installing these filters in hand dryers, the number of dispersed bacteria has been significantly reduced. Some bacteria, however, were still distributed — including potentially pathogenic ones.