The hygiene mythbuster

31 March 2015

This issue, intrepid columnist and Chemex International's scientific director Seán Derrig goes into the field to track down hot spots of faecal contamination

People have some very funny ideas about germs and where they lurk. And how you test for them. I was involved recently in a TV science program due for transmission later this year looking at – without giving too much away – levels of bacterial contamination in different locations. And specifically the sort of bacteria associated with, well, poo.

Sounds like a simple question but it’s complicated by the fact that over 80% of the 8,000-plus species of bacteria found in your colon can’t be grown in a lab and almost all of those that can are unable to tolerate oxygen. But there are a few organisms that we can culture easily that are used in many industries as a yardstick for faecal contamination.

So, picture the scene: We’re at the producer’s home to show the team what can and can’t be done and to give an idea what might work well on TV. But this is a pretty well-trodden path; there have been many studies looking at where faecal bugs end up and it’s pretty much everywhere. Well, everywhere except the toilet seat. Which – much to the producer’s horror – was where I started.

Toilet seats are pretty germ-free in the grand scheme of things – a simple fact my wife resolutely refuses to accept but true nonetheless. You’d be lucky to find even 50 bacteria per square inch. You can multiply that by 10 for a mobile phone, by 200 for a computer keyboard and by about 200,000 for a kitchen cloth or sponge. One US study found the ice served in 70% of fast food joints had more faecal bugs than the toilet water, let alone the seat. And over a decade the average mattress will double in weight due to poo produced by mites getting fat on the 10 million skin cells you shed every night.

After the toilet seat I went for the toothbrush which scored well: a toilet flush causes aerosol droplets so small they will linger in the air for ages. Until they join their friends on your toothbrush, obviously. And don’t get me started on reusable shopping bags. At least you wash your pants. Need I say more?

So, what grew in the lab was pretty much what I expected but it horrified the production crew. And given what we found in the dog’s bed and bowl I suspect none of them will be allowing their pets lick to their faces any more…