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"Fecal Matter on Your Shopping Cart Doesn't Matter"; A Microbiology Professor Speaks

A study of shopping carts has Americans scared, but a Cal Poly professor says everyone should chill out.

On Thursday, the University of Arizona released a Clorox-sponsored study that found 72 percent of shopping carts had fecal matter on them. It sounded icky, of course, but is it dangerous? We asked California Polytechnic State University professor of biology Pat Fidopiastis his thoughts on the research. What he had to say should put you at ease. In short, there are poop germs around you all the time, but, if you do a few simple things, you're probably going to be just fine.

As told to GOOD:

In my opinion, none of this means much unless you can show me a significant risk involved with coming in contact with a shopping cart. You might be able to say that "X percent" more kids get sick if they touch a shopping cart handle versus a bathroom door knob, for example. But what are the actual numbers? Is this like saying, "More people get struck by lightning if they walk around outside in a storm than those who stay in their homes"?

Regarding the E. coli: E. coli is merely an indicator that fecal contamination probably occurred, since E. coli is a common microbe in mammalian gut tracts. I emphasize "probably" because in warmer climates we're starting to realize that E. coli can persist in the environment and might not necessarily indicate recent fecal contamination. The old dogma was that E. coli doesn't persist, and therefore, if it's present, it must be from fresh feces. Nowadays, however, although there are deadly strains of E. coli that can kill in very small doses—as few as 10 cells of E. coli strain 0157:H7 under ideal condition can cause severe illness—I'm not aware of a single case of this microbe causing disease through any vehicle other than food (beef, etc.). Stomach acidity and other defenses make it really difficult for such small doses of microbes to cause problems, so usually it's only when microbes grow in food for a while that they can reach numbers sufficient to infect.

There are two camps on this issue with the shopping carts: Obviously those with a vested interest in scaring people (the folks at Clorox, for example), and the "hygiene hypothesis" types that feel we need to be exposed to all the bacteria possible in order to strengthen immunity. The ideal is somewhere in between. Personally, I think less about E. coli and bacteria and more about viruses that can be shed in feces along with E. coli, such as noroviruses (so called "cruise ship viruses"), polio virus (from someone who received the weakened strain in the oral polio vaccine—no longer really used in the U.S.), and hep A. But the odds are greatly in our favor that we'd never really need to know they're there.

I'm a surfer and I lived in Hawaii for six years. I surfed every day at breaks all over Oahu and never thought about sharks until a study came out in which some tiger sharks were tracked and found to come close to shore on a regular basis. I still surfed every day as before, the only difference was that now I was thinking about sharks. I have to admit that I'm a "grocery cart handle wiper," because it's really no real trouble to do and it will further minimize the already huge improbability of getting sick. But I'd never change my lifestyle in any more drastic way because of a study like the the grocery cart one, just as I still surfed after the shark study.

Students in my lab have shown that upwards of 30 percent of the noses they swabbed around campus tested positive for Staphylococcus aureus, a brutal pathogen that can cause a variety of diseases, including a foodborne intoxication characterized by intense vomiting. We've also discovered high levels of bacteria such as Pseudomonas aeruginosa (PA) on kitchen counter tops, in kitchen sponges, in hot tubs, and on cutting boards. PA causes horrific skin infections and is a leading bacterial cause of death in cystic fibrosis patients when it gets into the lungs. The point is that dangerous bacteria is always around us. As long as people don't freak out, but instead do the simple little things on a regular basis—washing your hands as well as those of your children after grocery shopping, microwaving wet sponges for a minute after each day, not putting anything on a cutting board that has been exposed to raw meat—they'll most likely be fine.

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