Scientists knock out "five-second rule"

The "five-second rule" — that allows us to eat dropped food if it's quickly scooped off the floor — is a bunch of nonsense, according to Clemson University food scientist Paul Dawson, who stirred up the long-debated issue in this month's National Geographic.

Though previous research has shown we may have up to a minute to rescue certain types of spilled food before it becomes contaminated, Dawson and his students made a strong case for the "zero-second rule." They found that salmonella and other bacteria can live up to four weeks on dry surfaces and be immediately transferred to food.

The zero-tolerance standard, however, conflicts with the findings by two Connecticut College student researchers who sprinkled apple slices and Skittles candies in the college dining hall and snack bar for five, 10, 30 and 60-second intervals. The apple slices picked up bacteria after one minute; nearly five minutes elapsed before the Skittles attracted any.

Still, most researchers agree that the critical thing is not time, but location. It's OK to brush off the bagel that fell from the stroller onto the sidewalk and give it to your screaming child, for example, because the pavement is cleaner than the kitchen floor in terms of the types of germs that cause illnesses, said Dr. Harley Rotbart, a professor of microbiology and pediatric infectious diseases at the University of Colorado School of Medicine.

"The kitchen floor, however, is probably a zero-second zone because the bacteria from uncooked meat and chicken juices are more hazardous than the 'soil' bacteria outside," said Rotbart. The bathroom floor is another zero-second zone because "it's a great potential source of bacteria and shorter-lived viruses that can cause gastrointestinal illness if ingested," said Rotbart, the author of "Germ Proof Your Kids."

100 billion: The number of bacteria in our mouths.

100 trillion: The number of bacteria in our gastrointestinal tracts.

2.5 billion: The number of bacteria found in one gram of garden soil.

7.2 billion: The number of germs in the average kitchen sponge.

25,000: The number of germs, per square inch, on an office telephone.

49: The number of germs, per square inch, on a toilet seat