Dr Donald Schaffner, a professor at the US-based Rutgers University, refers to research, which shows that there is no ‘safe amount of time’ for someone to pick a food item from the floor.

He told Gulf News via email: “Our research showed that no matter which foods, or which surfaces, even if exposed for a fraction of a second, there were always some experiments where at least one cell of the microorganisms we used were transferred to the food. Thus, our research has disproved the five second rule. There is no safe amount of time, which would guarantee no bacterial transfer.”

Their research involved adding bacteria on the surface of a variety of food items, so they could measure the transfer accurately. Dr Schaffner explained how different surfaces could affect the food differently.

He said: “If you were to drop food onto a sterile surface, since there would be no bacteria on the surface, you can safely eat the food with no risk. On the other hand, if you were to drop food onto a surface with even one cell of a pathogen, like Salmonella, even if that one cell transferred to the food, and you ate it, there is a possibility you would become sick.”

The situation is worse if it is a wet food item, such as watermelon, in comparison to something that is dry, like a potato crisp. In the first case scenario, all of the bacteria on the surface will transfer to the food as soon as the contact is made. “For other food products, you might see significantly more bacteria transferred after 20 seconds versus five seconds,” explains Dr Donald Schaffner.

That’s not it. The pace at which the bacteria transfers to the food differs based on the surface, too.

Ashley Isaac, an assistant instructor of Biology at New York University Abu Dhabi (NYUAD), said: “Any surface, hands, cooking utensils, food preparation surfaces or unwashed raw foods themselves, can serve as a reservoir for bacteria, some of which could be potential pathogens. Smooth surfaces are likely to transfer more bacteria than say a rough or bumpy corrugated surface or carpet, in which not all surfaces of the food item may be in contact with.”

He warns people to be careful when considering to eat something that has fallen on the floor, no matter how long it was there. He refers to studies that show that “bacteria can persist on surfaces for many days and have the potential to contaminate fallen food”.

“In general, proper food handling, storage, basic sanitation and hygiene are essential in the prevention of food-borne illnesses,” he added.