It almost happens in slow-motion. You fumble clumsily and all of the sudden that piece of food you were rocketing into your mouth is teaching you a lesson in the law of gravity. And as your food tumbles to the ground, your mind is working quickly to calculate how swiftly you can snatch it off the floor before it becomes “contaminated.” Unfortunately for you, the widely touted five-second rule for food doesn’t appear to hold up under the scrutiny of science.
A 2006 study conducted by Dr. Paul Dawson of Clemson University looked at the survival and transfer of Salmonella Typhimurium from wood, tile or carpet to bologna and bread. The study found that S. Typhimurium can survive up to a month on dry surfaces and can be transferred to foods almost immediately on contact. It demonstrated that bacterial transfer to food isn’t really determined by how long the food is in contact with the dirty surface, but by the sheer volume of bacteria on the surface itself. Location is key: dropping a granola bar on the sidewalk would be preferable to dropping it on your kitchen floor because the latter is more likely to breed illness-causing bacteria.
In the study, the surface also played a role in how thoroughly a piece of food collected bacteria. More than 99% of bacterial cells were transferred from tile to the bologna after five seconds of exposure. The transfer of bacteria from the wood to either food was similarly high, like tile. In stark contrast, the carpet transferred less than 1% of bacteria to the food.
The type of food that is dropped may also determine how quickly it becomes infected. This concept has yet to be studied and confirmed, but it is plausible that some foods would be more apt to collecting bacterial cells than others. For example, if you dropped an apple and a hard candy on the ground next to each other, the wet, sticky apple would likely pick up bacteria more quickly than the hard, dry piece of candy.
So now it’s finally time to quite that gross habit of eating things off the floor. No one thought it was cute before, and now we know that it’s unhealthy. The best way to remain prepared regardless is to keep the surfaces of your home and your hands clean.
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