What's better for limiting the spread of bacteria in washrooms: paper towels, or air dryers?
New research funded by a trade organisation of paper towel manufacturers suggests that towels spread less bacteria.
Previous studies have shown mixed results, some finding air dryers spread more bacteria and others showing they're as safe as towels. A review of past studies published in 2012 in the Mayo Clinic Proceedings suggested that in healthcare settings, at least, "paper towels should be recommended."
In the new study, jet air dryers spread 27 times the microbes as paper towels, and four times more microbes than warm-air machines, researchers said in a presentation last week in France at a meeting of the European Tissue Symposium, which sponsored the work.
Lead author Mark Wilcox and his colleagues had volunteers dip gloved hands into yogurt containing lactobacilli, a type of "friendly" bacteria. Then, the volunteers dried their hands using jet air dryers, warm air dryers, and paper towels.
The test was repeated 60 times over six weeks for 20 collections of each method.
From one meter away, the average airborne bacterial counts, measured in so-called colony-forming units, were 89.5 when the gloved hands were dried with jet air dryers, 18.7 using warm air dryers, and 2.2 from paper towels.
To assess the potential spread of bacteria visually, individuals dipped their gloved hands in black paint and wore white disposable suits backwards with the hoods covering their faces. When they dried their hands, there were 230 visible spots from the jet air driers and 130 from the warm air dryers. None were found on people who used paper towels.
Wilcox, who is a consultant/head of microbiology at Leeds Teaching Hospitals in the UK, pointed out in email to Reuters Health that drying hands thoroughly is an important way to avoid spreading bacteria to other people or surfaces.
"I had made the disconcerting observation that when using some jet air driers I could feel droplets hitting my face," said Wilcox of his interest in doing the study. "For an infection control doctor, a key principle is to reduce the risk of spread of microbes."
He and his coauthors say that more research is needed before anyone can assume the air dryers spread more germs than towels.
In email to Reuters Health, William Gagnon, vice president of marketing for Excel Dryer, Inc. in East Longmeadow, Massachusetts, pointed to studies that showed no difference in bacteria with the different drying methods and others that showed microbes on unused, recycled paper towels.
Benjamin Tanner, a microbiologist who is president and CEO of Antimicrobial Test Laboratories in Round Rock, Texas, criticised the new study for using gloved hands (which he said is unrealistic), paint spots and a high number of bacteria - and for failing to show any real health risk.
"A well done study would have measured levels of disease-causing organisms on the hands (which may have been done), then measured the number of those bacteria that are blown off as a result of drying," said Tanner in an email to Reuters Health.
Wilcox replies that the study "purposely contaminated hands with a high number of bacteria to represent poorly washed hands, and (we) have justified this decision in our publication."
Dr. John Segreti told Reuters Health by phone that the study is interesting and well done. "What they were trying to do was mimic someone who doesn't wash their hands carefully," said Segreti. "It wasn't intended as a real-life analysis."
But Segreti, who was not involved in the study, doesn't think bacteria from dryers are much of a health risk.
"In their conclusion, they have a lot of maybes . . . and I think you have to keep that in mind with this," said Segreti, an infectious disease specialist and hospital epidemiologist at Rush University Medical Center in Chicago.
Importantly, he said, "most of the pathogens people have on their skin are not spread by the airborne route but by direct (contact)."
"It's what's left on your hands after drying that is more important than what's aerosolized into the air," he said.
Segreti also said hospitals tend to use alcohol gel or foam on patient floors, not air dryers.
"Certainly (they're) in public restrooms all over the place and how that translates to transmission in the community is a different issue. I don't know of any outbreak yet that's been traced back to any of these," said Segreti.
Before last week's presentation in France, the study was online in August in the Journal of Hospital Infection.