With an unsettling *splat* your toast has once again landed butter-side down on the carpet. But it's not like you're going to waste another five minutes waiting for a replacement piece to brown. Heck no, just yell out "five second rule," pick that sucker up, brush off all that hair and lint and you're ready to eat, right? Science says no.
The most important thing to remember about the world around you is that everything is covered in germs, at all times. There are an estimated 100 billion in your mouth right now, another 100 trillion living in your digestive tract. As many as 25,000 germs crowd onto every square inch of your phone, though, and another 7.2 billion call your kitchen sponge home. Luckily, an overwhelming majority of these microscopic lifeforms either pay us no attention or actively work for our mutual benefit. The rest of them, though, can kick your ass.
It doesn't take much for food-borne pathogens like E. coli and Salmonella to infect your gut and wreak havoc on your bowels. In fact, fewer than 100 E. coli and less than 10 Salmonella bacteria constitute an infectious dose. And the body's natural defences, specifically the acidity of our saliva and stomach acid, aren't always enough to stamp out microscopic invaders. "Many viruses survive the low pH — in fact, they like it," explained University of Arizona microbiologist Charles Gerba to WebMD. "Viruses like hepatitis A and norovirus (stomach flu) survive well at low pH. So do bacteria like Salmonella. Any bacteria that infects the intestine can survive the low pH long enough to get to the intestine." And the intestine is where the real trouble starts.
When E. coli invades, specifically the Shiga toxin-producing E. coli (STEC) variety responsible for a majority of the quarter million E. coli infections in the US annually, patients typically suffer severe stomach cramps, bloody diarrhoea, and vomiting. If their immune system is compromised, the bacteria can also cause a life-threatening fever. And Salmonella isn't much better. According to the CDC:
Most persons infected with Salmonella develop diarrhoea, fever, and abdominal cramps 12 to 72 hours after infection. The illness usually lasts 4 to 7 days, and most persons recover without treatment. However, in some persons, the diarrhoea may be so severe that the patient needs to be hospitalised. In these patients, the Salmonella infection may spread from the intestines to the blood stream, and then to other body sites and can cause death unless the person is treated promptly with antibiotics. The elderly, infants, and those with impaired immune systems are more likely to have a severe illness.
Therefore, your best defence against severe intestinal discomfort and possible death is never letting germs in to begin with. That's something we're collectively terrible at. Particularly when it comes to our food. Especially particularly when we assume that picking up food quickly off the floor can somehow prevent pathogens from hopping on board.
The Five Second Rule is defined as:
An unwritten law dictating that if a food or other consumable item is dropped onto the floor, it may be picked up up and eaten within five seconds. The reasoning behind this is that dirt and germs take six seconds to transfer from one surface to another.
The origins of this superstition are still being debated; some credit Genghis Khan for first implementing the 12 to 20 hour rule for eating food from the ground (no, seriously; later generations would refine the timing down to the modern five seconds) and others credit the fast food industry as a means of reducing food waste, though both seem improbable.
The first scientific attempt to verify or dismiss the validity of the five second rule did not occur on the Discovery Channel, but rather at the University of Illinois at Urbana-Champaign by high school senior Jillian Clarke during a six-week internship back in 2003.
Her experiment started off with a startling discovery. "We were shocked," Meredith Agle, a Ph.D. candidate who helped conduct the experiment told Aces College News. They had been swabbing inch-square sections of floor around high-traffic areas on campus but they couldn't find enough germs to test with. "We didn't even find a countable number of bacteria on the floor. We thought we might have made a mistake, so we tried again with the same result. Then we went back to look for spore-forming organisms, such as Bacillus, something that would resist dry conditions, but we couldn't find any spores either."
Either bacteria don't occur naturally in Illinois or the university has a top notch cleaning crew, so the team created a controlled simulation using 2-inch squares of rough and smooth-sided tiles coated in an E. coli broth. Gummi Bears and biscuits were placed onto both surfaces for five seconds, then measured for the presence of pathogens. "We did see a transfer of germs before five seconds," Agle told WebMD. "We were dealing with a large number of cells."
Overall, this small scale-study made a number of interesting observations beyond the fact that falling food doesn't stun bacteria for any measurable amount of time: 70 per cent of women and 56 per cent of men queried admitted to invoking the rule and all those surveyed were more likely to invoke the rule for a piece of candy than they were for vegetables.
The Annals of Improbable Research honoured Clarke with the 2004 Ig Nobel Prize in public health for her pioneering work.
Since Clarke's first foray into fallen food, numerous research teams have taken up the helm and conducted their own surveys into the safety of eating things from the floor, with diametric results.
In 2007, Molly Goettsche and Nicole Moin, a pair cell and molecular biology students at Connecticut College, spread apple slices and Skittles across the floors of the college dining hall for predetermined intervals of 5, 10, 30, and 60 seconds. Their results suggested that bacteria wouldn't transfer to the apple for nearly a minute and the Skittles for nearly five. Apparently, bacteria don't naturally exist on the Connecticut College campus either.
The findings above were almost immediately countered in a study conducted by Clemson University food scientist Paul Dawson and his team of student researchers. In May of 2007, Dawson's team assembled and sterilised a variety of surface samples — tile, wood and nylon carpet — then coated them with Salmonella (with a density of several million bacteria per sq cm) in order to not only see how long the organisms survived on each, but also to see how effectively they could hop on a slice of bread or bologna.
The Clemson findings suggest that we should rename it the "zero second rule" because even after being left to dry for four weeks on the surfaces, the Salmonella were onto the bologna sandwich like white on rice in a glass of milk in a snowstorm in under a second. Leave the meat and bread there for five seconds, and the food picked up 150 to 8,000 bacteria. Leave it for a minute and the number increases tenfold. Tile and carpet reportedly gave up the most microorganisms, while wood transferred slightly fewer.
Bologna and bread are not the only things we eat from the floor, and not all foods pick up microbial hitchhikers as readily. A study conducted at Manchester Metropolitan University went beyond meat and bread to examine how effectively bread with jam, cooked pasta, a slice of ham, a plain cookie, and dried fruit picked up pathogens after being left on the ground for between three and ten seconds.
Turns out, the foods that are least healthy for humans are also poor conductors of germs. Those foods high in salt and sugar but low in water content — i.e. the ham, biscuits, and bread — showed little growth after a three second interval, while the relatively wet cooked pasta and dried fruit (which still contains a good amount of moisture) picked up a far larger number of bacteria including Klebsiella.
The team believes that the amount of water present in the food, which is essential to bacterial growth, is the main factor in transference rates. However water can work to your advantage as well. "At least, wash it first," Ruth Frechman, MA, RD, and spokeswoman for the American Dietetic Association told WebMD. "Bacteria are all over the place, and 10 types, including E. coli, cause food-borne illnesses, such as fever, diarrhoea, and flu-like symptoms."
Water content and timing aside, where you drop your food is critical to your chances of getting sick from then eating it. And it's not always where you expect. As Dr. Harley Rotbart University of Colorado School of Medicine explained to WebMD, pavements, while filthy in their own right, don't house the same food-based pathogens as a kitchen or restaurant floor would.
"The kitchen floor, however, is probably a zero-second zone because the bacteria from uncooked meat and chicken juices are more hazardous than the 'soil' bacteria outside," Rotbart stated.
The same goes for your bathroom, which is home to a number of gastrointestinal pathogens and virii. And the number one place you should never eat from, in or near: public restrooms. "About 93 per cent of the shoes we have tested have foecal bacteria on the bottom,"said Rotbart. "People track bacteria and viruses on their shoes all the time."
So remember, your floor may be "clean enough to eat off of" — but that doesn't mean you actually should. [Aces College News - NY Times - Wikipedia - LA Times - How Stuff Works - Clemson University - WebMD - Gizmodo - Daily Mail - Colorado State University - Connecticut College - Top Image: Joe Belanger / Shutterstock]