Well, we always knew that the five second rule was more of a guideline than a rule. It's been around a lot longer than germ theory. I am noodling a book about Genghis Khan and so I have been reading a lot of things about this mass-murdering sociopath. So when I saw what is apparently an annual puff piece from the mainstream media about the five second rule I was reminded about the fluid nature of its historical origins.
History, of course, is rather subjective. I imagine the 5 second rule was 5 days in prehistoric times, when food was harder to come by, so pinning down when it became a 5 second rule is just guessing. Genghis Khan was a rather scientific guy for being a homicidal rapist maniac so he had his own notions on how long food could be on the ground and still be safe. And he was right - obviously eating food off the ground was a lot safer than going to war and he was always going to war. And organic food buyers today think food can sit in pesticides forever, as long as they are organic pesticides.
Even an M&M tried to work the folklore in this 1999 commercial:
Germs can attach themselves, we have known that for a while. But for this study they wanted to find out how long a 'food on the floor' rule might be. They used some carrots (and then a control group of one carrot kept clean, though I have no idea why they think they need a control group or what they consider 'clean') and found that all the surfaces couldn't keep food clean for 5 seconds. Some were worse than others. Countertops fared more poorly than a carpet. No one saw that coming.
Now, Clorox is in the cleaning products business so the results are obviously correct but that doesn't make them valuable. There is a big difference between picking up a grape from a reasonable floor versus a peanut butter sandwich that lands face down in a house with pets. If you drop a Twinkie, the long-term effects from the Twinkie are not the germs.
Did Clorox and the San Diego researchers examine how long Clorox bleach lasts on countertops after cleaning and can be transmitted to food? Errr, no, that would just be silly.
Hewitt KM, Gerba CP, Maxwell SL, Kelley ST (2012) Office Space Bacterial Abundance and Diversity in Three Metropolitan Areas. PLoS ONE 7(5): e37849. doi:10.1371/journal.pone.0037849