The Five-Second Rule Explored, or How Dirty Is That Bologna? – New York Times
Professor Dawson and colleagues placed test food slices onto salmonella-painted surfaces for varying lengths of time, and counted how many live bacteria were transferred to the food.
On surfaces that had been contaminated eight hours earlier, slices of bologna and bread left for five seconds took up from 150 to 8,000 bacteria. Left for a full minute, slices collected about 10 times more than that from the tile and carpet, though a lower number from the wood.
The infectious dose, the smallest number of bacteria that can actually cause illness, is as few as 10 for some salmonellas, fewer than 100 for the deadly strain of E. coli.
Of course we can never know for sure how many harmful microbes there are on any surface. But we know enough now to formulate the five-second rule, version 2.0: If you drop a piece of food, pick it up quickly, take five seconds to recall that just a few bacteria can make you sick, then take a few more to think about where you dropped it and whether or not it’s worth eating.