Spending most of my time in a high school, I’m always hearing references to the “five second rule.” I’ve always said if there was a five second rule, it shouldn’t apply with respect to the floors of a school. Looks like I’m getting scientific backup:

“A dropped item is immediately contaminated and can’t really be sanitized,” says Jorge Parada, MD, MPH, FACP, FIDSA, medical director of the infection prevention and control program at Loyola University Health System. “When it comes to folklore, the ‘five-second rule’ should be replaced with ‘when in doubt, throw it out’.”
All items that come into contact with a surface pick up bacteria (and dirt!). How much bacteria and what kind of microbes depends on the object dropped and the surface it is dropped upon, he says.