Food Safety in the Time of COVID-19: The 5 second rule

With so many meals consumed at home these days, there are bound to be mishaps, such as a spilled glass of milk or a sandwich dropped on the floor. So it’s a good time to revisit the age-old 5-second rule. This isn’t the in-bounding rule in basketball, but a food hygiene standard in some households that states that there is a defined window where it is permissible to pick up food (or sometimes cutlery) after it has been dropped to the floor or ground. Some even argue that you have at least 10-seconds before your dessert cookie is contaminated enough to direct it towards the trash.

What does the science tell us? Several scientific studies have looked at this phenomenon. The most comprehensive was work done by researchers at Rutgers University in 2016. In the study, researchers dropped bread, buttered bread, watermelon slices and strawberry gummies from a height of five inches on to a surface: low-pile carpet, ceramic tile, stainless steel and wood. The surfaces were slathered with a bacteria Enterobacter aerogenes as a ‘stand in’ for pathogens such as Salmonella. The food was left on the surface in intervals of 5, 30 or 300 seconds and the scientists assessed the amount of E. aerogenes transferred between surface and food.

The results:

  • Bacteria easily transferred to moist foods like watermelon, even 5 seconds was too much.
  • While carpet transferred fewer bacteria than stainless steel or tile, it still served as a contaminating surface if left too long. Results with wood were hard to ‘nail down’.
  • Bacteria that remained in carpet were difficult to remove on cleaning.

What should you do?  The researchers urge consumers to not place carpeting in the kitchen and, while the results are mixed, for safety-sake we shouldn’t be eating food that has been dropped onto the floor. Dr. Don Schaffner, a Rutgers University food scientist and author of the study noted: “The five-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food. Bacteria can contaminate instantaneously.”  Stay well and food-safe, Barb