Surprisingly, serious researchers have found that following the “five-second rule” when food items are dropped on the floor isn’t the worst thing a restaurant might do from a food safety perspective. What might be just as bad, or perhaps worse: routinely exposing customers to bacteria-laden menus, tabletop items and even lemon slices.

The five-second rule refers to the accepted wisdom that food that falls on the floor is OK to eat if picked up within five seconds. The idea seems like wishful thinking that would quickly be disproven by a rudimentary scientific investigation, or even by the application of common sense. But the results of a study performed by microbiology researchers at Aston University in Birmingham, England, show that the five-second rule isn’t too far off the mark.

Their study involved dropping six types of food—toast, pasta, biscuits, ham, dried fruit and a sticky dessert—onto various types of flooring, leaving them in contact with the floor surface for between three and thirty seconds. The foods were then checked for the presence of E. coli or staphylococcus aureus, common causes of food poisoning in restaurant settings.

The results show that both the length of time the food item is on the floor and the type of surface with which it comes into contact matter. An exposure time of five seconds or less significantly lowers the chance of bacterial transfer from floor to food. Laminate or tile surfaces are more conducive to bacterial transfer than carpeting.

Separately, the researchers surveyed consumers about whether they would eat food that had fallen on the floor. Eighty-seven percent of people said they would, 55 percent of them being women. Note that the researchers did not ask whether they would eat in restaurants that followed this practice, when we’re betting the number of people who were OK with this practice would be near, or at, zero.

In a perfect world, food never falls on a restaurant kitchen floor, and food cost considerations never come into play when cooks contemplate washing or wiping a food item and then serving, it instead of throwing it away. Just as ideally, servers and hosts or hostesses would sanitize menus after each use by a customer.

But do they? Cleaning system company Kaivac says that menus can harbor more harmful germs and bacteria than perhaps any other surface in a restaurant, even the floor.

The company points to a study conducted by team of scientists on behalf of ABC television show Good Morning America. Investigating 12 restaurants, the team found that the menus they collected had an average bacterial count of 185,000 per square centimeter, “far more than a toilet seat,” Kaivac notes.

Seem far-fetched? A more rigorous study performed by Clemson University graduate student Ibtehal Alsallaiy, Bacterial Recovery, Transfer to Hands and Survival on Restaurant Menus, found that bacteria do indeed transfer from a menu to the consumer's hands and that bacteria can survive on menus even after 48 hours.

This research raises a question for restaurant operators: Who’s wiping off the menus at your restaurant, and when?

Other trouble spots identified by Kaivac:

Seats: “They are rarely cleaned, and when they are, they are often quickly wiped down using a soiled towel,” Kaivac’s Matt Morrison says.
Ketchup bottles: “Scores of people touch these, and they are rarely wiped down with an antibiotic cleaner.”
Lemon slices: One study found that lemon slices are often not properly washed. As a result, 70 percent of lemon slices used in drinks or on dishes in restaurants carried potentially harmful microorganisms.

Most restaurants already go to great lengths to protect customers from potential exposure to e. coli or staph. It might make sense to stress the importance of cleaning and sanitizing menus and tabletop items at your next front-of-the house meeting.