Again with the headlines: “The ‘5-second rule’ is disproved in new study”.
And, again, checking the veracity of their knowledge translation distillation: not exactly.
These authors placed four different foods (watermelon, bread, buttered bread, and gummy candy[Haribo, Strawberries]) on four different surfaces (steel, tile, wood and carpet). They let the food stay in contact with the surface for <1 second, 5 seconds, 30 seconds, or 300 seconds. However, where this study falls off the generalizability wagon: each surface was pre-coated with bacteria-rich broth.
So, yes, in their study, even instant contact was adequate to transfer some bacteria from surface to food. Five seconds quite obviously transferred plenty of bacteria. Otherwise, the amount of bacteria transferred was roughly related to moisture in the food item and surface area in direct contact.
But, is the “5-second rule” obsolete? Hardly. Consider the context of history – where humans have been eating in less sanitary situations for hundreds of thousands of years. Then, chances are your hands are more likely to contaminate your food than the floor in your house. So, food that has been dropped on most clean floors may pick up some bacteria – but these authors’ results are only a surrogate for multifactorial confounded potential downstream harms.
However, if your floor is coated with a thriving culture of pathogenic bacteria – all bets are off.
“Longer Contact Times Increase Cross-Contamination of Enterobacter aerogenes from Surfaces to Food”
http://aem.asm.org/content/early/2016/08/15/AEM.01838-16.abstract