The idea that food is safe to eat off the floor if you pick it up quickly is not accurate.
A study showed that in some cases, bacteria takes less than a second to transfer to food. The longer food was allowed to stay on a surface, the more bacteria was transferred to the food. The higher the moisture, the higher the risk of transfer.

The 5-second rule

Bacteria travel through moisture. Wet food like watermelon will pick up the most bacteria, while less sticky food like gummy candies picks up the least. Regarding the surface, carpet has a lower rate of bacteria transfer to food than other surfaces. 
The risk of illness from eating food that has fallen on the floor will depend on factors such as prevalence, concentration and type of organism, moisture of the food, the nature of the surface, and the length of time the food was in contact with the surface.

The 5-second rule

Still Good? 5-Second Rule a Myth, Study Finds | Live Science

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