Biometric sensors no dirtier than doorknobs, study finds

For the study, Blomeke's team examined the bacterial recovery and transfer from three types of biometric sensors: fingerprint, hand-geometry and vein-recognition devices. Each sensor was tested separately with two kinds of bacteria: Staphylococcus aureus, a common cause of blood and skin infections, and Escherichia coli, commonly known as E. coli, which can cause diarrhea, urinary tract infections and meningitis.

To test how well the bacteria could survive on a biometric device, the surfaces were first sterilized to kill existing bacteria, then coated with a bacteria culture. Testers used sterilized gloves to touch the biometric device surface after five, 20, 40 and 60 minutes to measure how many of the bacteria were still alive and could be transferred. Testers first touched the device surface, then a sterile plate or Petri dish containing growth media to allow any bacteria present to be more easily examined. The solution on the plate was allowed to grow for 24 hours at 37 degrees Celsius (approximately 99 degrees Fahrenheit).

The next step was to test for bacterial transfer from the biometric device. To do this, the devices were sterilized, then testers wearing sterilized gloves touched the device surface and a sterile plate to measure how many bacteria were present before it was contaminated. Next, the device surfaces were contaminated with one species of bacteria at a time, and testers wearing sterilized gloves touched the device surface, then touched a sterile plate containing growth media 50 times. Just as in the other test, the solution was allowed to grow overnight to quantify the number of live cells recovered from touching the contaminated device.

Researchers found that E. coli survived on the devices slightly longer than staph bacteria, but within 20 minutes, nearly all of the bacteria had died on all three devices.

Finally, a metal doorknob was tested with the same methods. Researchers found that the transfer of bacteria from the doorknob to another surface was nearly identical to that of the biometric devices. Blomeke said that on the doorknob, as well as on the three biometric devices, the majority of bacteria was transferred within the first 10 touches.

"What we can take away from this is that no matter what kind of a surface it is, if it is contaminated, the more it is touched, the cleaner the surface becomes," she said. "Of course, the bacteria are moved to the hand. But it's important to remember that there are naturally occurring bacteria on everyone's hands, and hundreds or even thousands of cells would have to enter the body - through a cut in the skin or from mucous tissues - to make a person sick."