For some perspective on yesterday’s story about MRSA and other bugs found on BART train seats, let’s turn to Good Magazine, which interviews microbiologist Pat Fidopiastis about a separate study, funded by Clorox, which found bacteria on shopping cart handles. Fidopiastis writes:

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”?

That’s a smart way to handle just about anything in life, but especially claims about bacteria in public places. Not least because most bacteria are harmless, and even those that are pathogenic – even highly pathogenic – tend to be easy for your body to fight off (if you’re not immunocompromised or otherwise at high risk of infection to begin with). Fidopiastis explains that this is especially true of E. coli, which used to be taken as an indicator of fecal contamination, but now:

…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 [or BART seats, presumably]: 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. …

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 [are] 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.

He doesn’t mention this, but antibacterial soaps and the ubiquitous antibacterial gels may be doing more harm than good. The antibacterial soaps are no more effective than regular soap, and contain an antibiotic that accumulates in streams, promoting antibiotic resistance (if you can’t access the paper, here’s the take home message: “Although the number of studies elucidating the association between triclosan resistance and resistance to other antimicrobials in clinical isolates has been limited, recent laboratory studies have confirmed the potential for such a link in Escherichia coli and Salmonella enterica. Thus, widespread use of triclosan may represent a potential public health risk in regard to development of concomitant resistance to clinically important antimicrobials”).

So wash your hands now and then with regular soap, and don’t get to worked up.