Harold McGee writes in the N.Y. Times today that a recent paper from Clemson University researchers accompanied by six graphs, two tables and equations whose terms include “bologna” and “carpet,” is a thorough microbiological study of the five-second rule: the idea that if you pick up a dropped piece of food before you can count to five, it’s O.K. to eat it.

http://www.nytimes.com/2007/05/09/dining/09curi.html?_r=2&8dpc&oref=slogin&oref=slogin

McGee says he first heard about the rule from his then-young children and thought it was just a way of having fun at snack time and lunch. His daughter now tells McGee that fun was part of it, but they knew they were playing with “germs.”

We’re reminded about germs on food whenever there’s an outbreak of E. coli or salmonella, and whenever we read the labels on packages of uncooked meat. But we don’t have much occasion to think about the everyday practice of retrieving and eating dropped pieces of food.
Microbes are everywhere around us, not just on floors. They thrive in wet kitchen sponges and end up on freshly wiped countertops.

McGee says he learned from the Clemson study that the true pioneer of five-second research was Jillian Clarke, a high-school intern at the University of Illinois in 2003. Ms. Clarke conducted a survey and found that slightly more than half of the men and 70 percent of the women knew of the five-second rule, and many said they followed it.

She did an experiment by contaminating ceramic tiles with E. coli, placing gummy bears and cookies on the tiles for the statutory five seconds, and then analyzing the foods. They had become contaminated with bacteria.

For performing this first test of the five-second rule, Ms. Clarke was recognized by the Annals of Improbable Research with the 2004 Ig Nobel Prize in public health.
It’s not surprising that food dropped onto bacteria would collect some bacteria. But how many? Does it collect more as the seconds tick by? Enough to make you sick?
Prof. Paul L. Dawson and his colleagues at Clemson used salmonella and tested tile, wood flooring and nylon carpet using slices of bread and bologna.
First the researchers measured how long bacteria could survive on the surfaces. They applied salmonella broth in doses of several million bacteria per square centimeter, a number typical of badly contaminated food.

Professor Dawson and colleagues then 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.

McGee says that quick retrieval does mean fewer bacteria, but it’s no guarantee of safety. True, Jillian Clarke found that the number of bacteria on the floor at the University of Illinois was so low it couldn’t be measured, and the Clemson researchers resorted to extremely high contamination levels for their tests. But even if a floor — or a countertop, or wrapper — carried only a thousandth the number of bacteria applied by the researchers, the piece of food would be likely to pick up several bacteria.

The abstract for the original paper can be found at:
http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2672.2006.03171.x