Professor Donald W. Schaffner, a food microbiologist at Rutgers University in New Jersey, 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 — “Is the five-second rule real?” — appeared online this month in the American Society for Microbiology’s journal, Applied and Environmental Microbiology.

Researchers at Aston University’s School of Life and Health Sciences in England reported in 2014 that food picked up a few seconds after being dropped is “less likely to contain bacteria than if it is left for longer periods of time,” giving rise to news accounts suggesting that eating the food might be harmless. Those findings, and research done at the University of Illinois in 2003, did not appear in a peer-reviewed journal, Professor Schaffner noted.