(Aaron drops piece of food)

Aaron Carroll: One, two, three, four, five.  Some people would have you believe that this food is safe, but that food is not, all because of some arbitrary five second rule.  Now I'm not gonna eat this, because that floor is gross and bologna is gross and because of science, because the five second rule isn't real.  This is Healthcare Triage.

(Healthcare Triage intro plays)

So evidently there's a new study out of Aston University in the United Kingdom claiming that the five second rule is true.  They claim that students examined how e.coli and staph aureus move from carpet, laminate, and tiled surfaces to toast, pasta, biscuits, and sticky sweets.  When they were in contact from three to 30 seconds.  They claim that time is a significant factor and how much bacteria transfer when food is in contact with the floor and that how long it's in contact is related to how much bacteria move.  

Where to start with this?  First of all, I've scoured the internet, and I can't find the actual study results.  I can find a press release from Aston University's School of Life and Health Sciences, but I can't find the actual study.  I can't examine the methods, I can't see what statistical tests they performed, I can't tell if the results are clinically significant.  To be honest, I'm somewhat appalled that without this, the media ran it so heavily.  Almost every single major media outlet reported on this breathlessly.  I'm especially skeptical because good research already exists on this subject.

Jillian Clark won the public health Ignoble Award in 2004 at Harvard University for her work showing that many foods were significantly contaminated with e.coli after brief contact with tile.  She also found that floors were, in general, rarely contaminated with bacteria, but the main take-home point here is that there's no magic about five seconds--food either got contaminated or it didn't.  But there's an actual peer reviewed study on the subject, published in The Journal of Applied Microbiology in 2007.  Food scientists conducted three experiments to find out what happens when the five second rule comes up against salmonella, a fairly common but nasty bacterium that can cause vomiting and diarrhea.  First, they tested how well salmonella survived on various surfaces.  They found the bacteria were still alive after four weeks on dry wood, tile, or carpet, and enough of the bacteria survived to be able to transfer it to food.  Next, they tested how much time it took for the bacteria to transfer from these different floor surfaces to bologna or bread.  Over 99% of the bacterial cells transferred from the tile to the bologna after just five seconds of the bologna hitting the floor.  Transfer from wood was a bit slower, up to 68% of the bacteria were transferred, and transfer from carpet was actually pretty rare, with less than half of a percent of bacteria transferring to bologna.  When bacteria did transfer, they moved to the food almost immediately upon contact.  By five seconds, it was way too late.  Of course, in all these cases, the bologna was unfit to eat before it hit the floor, because bologna is gross.  

Other bacteria, like campylobacter and salmonella, can survive well on formica, tile, stainless steel, wood, and cotton cloths.  If you listen to microbiologists, you can never be too careful about cleaning things up in the kitchen, and you also can't trust the five second rule.  Bacteria that can make you sick can survive on the floor or other surfaces for a long time, and they can contaminate other foods that touch them for only just a few seconds.  

But bacteria aren't the only thing that can make you sick when food hits the floor.  Another peer reviewed study of pesticides was published in the Journal of Exposure Analysis and Environmental Epidemiology in 2003.  They found that toxic chemicals can transfer to foods like apples, cheese, and of course, bologna.  Pesticides do seem to take a little longer to transfer than bacteria though.  The average pesticide was only one percent efficient in transferring over to the food at the one minute mark, but up to 83% transferred if it was left on the floor for 60 minutes.  Don't try to invoke the one hour rule.  

Applying more force to the food, like throwing it against the floor, also resulted in more pesticide getting on the food--up to 70% at ten minutes on hardwood flooring when bologna was squished with a 1500 gram force.  But again, no magic with five seconds--either stuff transfers or it doesn't.  

Let me say that I'm not suggesting that you should panic about food that hits the floor, to be honest, I'm not terribly squeamish about eating food that's fallen, the human body is pretty good at fighting off a lot of germs, but what I hope you'll stop doing is believing that there's some protective effect of time.  No one is studying the clinical effectiveness of this--they're only studying efficacy, bacteria counts (as we discussed in our episode on antibacterial soap), there's no proof, none, that you're less likely to get sick if you get to the food in any amount of time.  If you don't think the floor is safe, then don't eat any food that hits it, no matter how fast you get to it.  If you don't care about the floor, then don't rush, 10 seconds is really no worse than five.