Arstechnica post pointed out in April. Their conclusion: them electric hot-air driers? They suck! In particular they suck in a selection of fecal coliforms from the flushing aerosols, concentrate them, warm them to blood temperature and then blow them all over your hands. After which you go and eat your dinner? I don't think so, and I try to have a scrap of towel at work so I can avoid using the drier or the seat of my pants.
The original study Deposition of Bacteria and Bacterial Spores by Bathroom Hot Air Hand Dryers out of UConn, Farmington, is paywalled but you can read the abstract at PubMed. They sampled the outblow from several bathrooms [both M & F] by holding a Petri dish open in the airflow for 30 seconds. They caught between 20 and 60 colony-forming units CFUs = bacteria on each plate. This was several times higher than the catch on Petri dishes left out on the bathroom counter next to a regular fan to circulate the miasma. They also found that the interior surfaces of the hand-driers were clean, so the CFUs were likely a sampling+concentration from the ambient air. High efficiency particulate air HEPA filters reduced but did not entirely eliminate the contamination. HEPA filters are designed to catch 99.97% of all particles that pass through the multi-layered device. Clearly 0.03% of the bacteria are enough to make a few colonies on a plate.
Here's an earlier Arstechnica slap at Dyson Airblades for helping to spread viruses: especially at heights equivalent to a small child's face. Original study out of U.Westminster, UK [abstract] also paywalled. These new-fangled over-tech Airblades delivered 1000x more viruses than plain old paper towels. That's kind of interesting because economists and statisticians are trained in risk-assessment to reconcile the incommensurate. How do you set off the loss to the planet of sending thousands of tonnes of paper towels to land-fill against a cohort of children having snot-virus blown at them? You can do a QALY analysis on the viral-load aspects but how do you set that against the cost of using paper towels now to the planet and the as-yet-unborn small children.
The answer really is to get an old cotton shirt, cut two neat squares out of the back, hem it, embroider your loved-one's name or initials in the corner and <presto> your Christmas presents are all sorted. If you cannot follow my instructions here is a fully illustrated protocol.