Every parent of small children is an amateur microbiologist.
A gummy treat drops on the floor of a public restroom: Contaminated!
At home, we run some rough mental calculus about the apple slice that fell on the living room floor: I just mopped, so it's ... probably fine?
We make these split-second judgments with little more than intuition and a vague sense that the world is teeming with bacteria and viruses. But a new book out this week, co-authored by Clemson University professor Paul Dawson, lends some actual expertise and experimental rigor to the nagging food-safety questions we've all been wondering about.
In stores Nov. 6 from publisher W.W. Norton & Company, Dawson and co-author Brian Sheldon's book "Did You Just Eat That?" busts a few myths and explains some hard science in laymen's terms.
Dawson has a Ph.D in food science and conducts some of his experiments with the help of undergraduate students through Clemson's Creative Inquiry program. You might have already heard the outcome one of their best-known experiments from 2006: The five-second rule is nothing more than an old wives' tale; germs are spread almost immediately upon contact.
By dropping a variety of foods on tile, wood and carpet surfaces infected with Salmonella typhimurium, Dawson and his team determined that the cleanliness of the surface is the biggest factor in whether a food item gets contaminated.
Dawson got a flood of responses after his research was picked up on NPR quiz shows and an episode of "MythBusters." Many of the comments came from parents, he told me in a phone interview last week. Some thanked him for settling a debate they'd been having with a spouse, while others shrugged off the science.
"People said, 'You're making things too clean, I grew up eating this, that and the other and I never got sick,'" Dawson said.
And it's true, you could eat food off the floor your entire life and never get food poisoning. In the book, Dawson shies away from directly telling people what to do, but he compares eating food off the floor to driving a car without a seat belt: Just because you haven't been hurt doesn't mean it's safe or wise.
"I don’t want to make people germaphobes," Dawson said. "On the other hand, there are circumstances where you should have a little caution."
Thumbing through Dawson's book last week, I found myself dog-earing pages that I knew would come in handy as a parent of young kids. Some chapters, like the one about beer pong, felt more like academic questions at this stage in my life. But the chapter on birthday cake felt like it was written just for me.
Have you ever thought about the fine mist of spittle that comes out of your kid's mouth when she blows out the candles on a frosted cake? I have, and so has Dawson, apparently. In an experimental design meant to mimic all the particulars of a birthday party, he had participants take a whiff of hot pizza and then eat a slice to get their salivary glands pumping. Candles were lit and placed in a layer of icing, and each participant blew until the candles were extinguished.
After scraping the spit-contaminated icing into a Stomacher bag meant to simulate the mixing action in your stomach, the scientists ran some tests and found that blowing out candles resulted in a population of bacteria 15 times higher than in a control sample of untouched icing.
Now, it's up to you what you do with that knowledge. If it's just you and the kids, odds are you're already sharing a lot of germs in your day-to-day life. Dawson urged me to consider group dynamics, though.
"If someone’s coughing and sick and overtly ill, you don’t want them blowing the birthday candles out. On the other hand, as we know, people can be carriers and not be overtly ill, so that may not be a great practice if you have your 90-year-old grandmother or grandfather there eating cake," he said.
Equally eye-opening was a chapter on the all-American tradition of sharing a tub of popcorn at the movie theater. Dawson traces the romance of popcorn and film back to the Great Depression of the 1930s, when movie house proprietors realized it was a cheap snack they could sell at a profit.
Dawson's team of scientists tested this one out by spritzing participants' hands with a nice layer of Escherichia coli and having them grab handfuls of popcorn from a sterile bowl. The more handfuls they took, the more infected the remaining popcorn became.
"By the time you're scraping the bottom of the bag," he wrote, "you might as well be kissing the person sharing the bag with you."
Dawson also brought up the possibility of self-contamination: As you buy your ticket, open doors or slide your hand along handrails on the way to your seat, you're picking up all sorts of passengers that can then transfer straight to your popcorn and into your mouth.
"That's an example of a pretty ripe situation," he said.
I asked Dawson if it might be a good prophylactic measure to bring a bottle of hand sanitizer so my kids can scrub their hands once we get to our seats. He said it couldn't hurt.
But when it comes to safeguarding against grubby little fingers, he offered one bit of timeless advice: Wash your hands. Do it often, and do it thoroughly, especially if you're about to eat.
In Dawson's view, the fear of "superbugs" that develop a resistance to antimicrobial soap is a bit overblown. He's more worried about the overuse of antibiotics.
"Alcohol or antimicrobial soaps are probably better as far as effectiveness. But what really is effective is scrubbing and washing and getting them off your hands," he said.
But you already knew that.