Over two years, the team tested a whole lot of elements to get a whole lot of measurements— nearly three thousand to be exact— and concluded that, no matter how briefly food touches a surface, it still picks up bacteria "instantaneously". However, what you drop where and how long it stays there matters. According to The New York Times, the study showed the longer food was left on the floor, the more gunk it picked up. It also found that watery food like watermelon sucked up the most bacteria, and carpet transferred less bacteria than tile or stainless steel, while wood varied.
Rico says that's too bad, as he's been known to eat stuff (as have you, admit it) that was on the floor a lot longer than five seconds...