The ‘five-second rule’ is untrue, study finds

YOU may think your floors are so clean you can eat off them, but a new study debunking the so-called five-second rule would suggest otherwise.

Professor Donald Schaffner, a food microbiologist, said a two-year study he led concluded that no matter how fast you pick up food that falls on the floor, you will pick up bacteria with it.

The findings in the report appeared online this month in the American Society for Microbiology’s journal.

Schaffner tested four surfaces – stainless steel, ceramic tile, wood and carpet – and four different foods: cut watermelon, bread, buttered bread and gummy candy, dropped from a height of 13 centimetres onto surfaces treated with a salmonella-like bacterium.

The researchers tested four contact times. A total of 128 possible combinations of surface, food and seconds were replicated 20 times each.

The research found t hat t he f ivesecond rule has some validity in that longer contact times resulted in transfer of more bacteria. But no fallen food escaped contamination completely. “Bacteria can contaminate instantaneously,” Schaf f ner sa id in a news release.

Carpet had a very low rate of transmission of bacteria compared with tile and stainless steel; transfer rates from wood varied.

The composition of the food and the surface on which it falls matter as much if not more than the length of time it remains on the floor, the study found. Watermelon, with its moisture, drew the highest rate of contamination and the gummies the least.

BRIAN HARKIN/THE NEW YORK TIMES Food dropped on the ground can be contaminated with bacteria instantly, regardless of how fast you pick it up, a study recently concluded.

PETER PARKS/AFP A magpie bird sits in a tree in Sydney.