Well, I'm tired of having that BBC page as the lead post on my blog, so I guess it's time to offer another glimpse into a dark corner of my brain.
Here's something I think about whenever there is lots of food sitting out for picnics, cookouts, holiday parties, etc. This means I'll be thinking about it a lot in November and December, since they are the months that are most packed full of this sort of thing out of the whole circular counter-clockwise running year.
Imagine a food storage container, virtually any kind that has a lid (as represented by figure A, depicting the container with the lid sitting next to it.) It could contain a casserole, or cookies, or corn pudding. You worked hard on the food, using your nice clean kitchen and nice clean cookware, and you washed your hands before handling it.
You put the food in it and close the lid. The food is now protected. Then you put it in your refrigerator, where the bottom of the container sits in whatever has spilled, dripped, or leaked onto the shelf since the last time you cleaned the refrigerator. Then you take it out again to bring to your Christmas party, or Holiday brunch, or whatever, and in the process you sit it on your kitchen counter, then on your dining room table. You carry it in your hands, then your three-year-old carries it for a few minutes, then you sit it on your car hood as you load stuff into the car. Then you sit it on your car seat or in your car trunk. Then you carry it into the party, where it sits on someone else's table, but before you sit it down their dog licks it a few times, then people bring more food and your container gets slid around and moved from place to place to make room.
Stuff gets spilled on the table: cookie crumbs, gravy, juice, pieces of ham, frosting (note the brown crud on the table in figure B.)
The outside of the container it now pretty much like your kitchen floor or your car hood.
This doesn't matter, though! Your food is still in the container. It is protected.
Then the container gets opened up. People eat out of it. It's just the way it works, everyone is okay with it, people reach in and pick up cookies, or use the spoon to scoop out the casserole, or whatever. That's person-to-person contact, with risks minimized by hand-washing perhaps, but everyone knows it's happening and you just deal with it.
But here is the thing that I always notice: People take the lids off the containers and put the lids, upside-down, underneath. The inside of the container lid is now flush against the bottom of your food container. The inside of the container lid is now the same as the upholstery of the trunk of your car.
So then the party wraps up, and everyone puts the lids back on their containers. The food is now stored with everything the bottom of your container has touched. (figure C.)
Why not just go around licking kitchen floors?
I know it's silly. I really don't care that much; I mean, I'd wrestle a chocolate chip cookie from a dog's mouth. I do, in fact, eat things that fall on the floor on a fairly regular basis, even though I know that the 5-second rule is a load of baloney. It's just something I think about, every time I see it occur.