You’ve probably heard that if you drop a piece of food on the floor and pick it up within five seconds, it’s okay to eat because germs hadn’t had enough time to get to it. (Personally I’ve always used a three-second rule, with a five-second corollary for chocolate.)
In a new study in the journal Applied and Environmental Microbiology, Robyn Miranda and Donald Schaffner of Rutgers University reported finding only three studies on this subject, and two of those were shared via press releases (which really isn’t publication). So they came up with their own experiment, leaving “watermelon, bread, bread with butter and gummy candy” on a variety of surfaces contaminated with Enterobacter aerogenes, a bacteria “with attachment characteristics similar to Salmonella,” for one, five, 10, or 300 seconds. Disappointingly, they found it took less than a second for some bacteria to transfer.
On a more positive and predictable note, a longer time in contact with the contaminated surface meant more bacteria transfer and a higher chance of some sort of infection in a real-world setting. In other words, it does help to grab the item more quickly. Plus other factors, like the food itself and the type of surface area, are also very important. For example, carpet has very low transfer rates, with higher rates for tile and stainless steel, and transfer rates from wood were variable.
In conclusion, “The 5-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food.” So to be safe, it’s best not to eat anything off the floor. But who wants a completely risk-free life?