It doesn’t really matter how long food is on the floor, it’s likely to collect the same amount of bacteria. Flickr/bark

“As a food microbiologist, I have always been amazed at people’s belief in the three- or five-second rule. It goes something like this: if you retrieve food dropped on the floor or another surface within three or five seconds, it won’t yet be contaminated with bacteria.

“Okay, it might just be wishful thinking. Or a handy excuse not to throw otherwise good food in the bin. But it really doesn’t add up.

“Let’s look at the facts. Disease-causing bacteria (known as pathogenic bacteria) and other microorganisms (such as viruses) are potentially everywhere and can be remarkably virulent. So logically, it would be an easy task for a microorganism to attach itself to a surface, especially to a moist piece of food.

“A 2007 study Journal of Applied Microbiology paper from a team at Clemson University in the United States, tested the five-second rule on tile, wood and carpet. They contaminated the three surfaces with a high level of Salmonella Typhimurium and looked at the rate in which the bacteria transferred to bread and sausages, over a period of 24 hours.

“They found the most significant variable in the transfer rates from all three surfaces was not the length of time it had contact with the food. The three testing times (five, 30 or 60 seconds) made little difference in the rate of bacterial transfer.

“The length of time the bacteria had been on the surface prior to contact with the food mattered more. Four hours after contamination, the same amount of bacteria remained on the carpet, while rates of bacteria on the tile and wood were slightly lower.

“But another study, on bacteria in the manufacturing environment, found that the longer the food was exposed to a contaminated surface, the more bacteria it accumulated. As did an investigation on transfer between meat surfaces. Click here to continue reading this article from The Conversation.