One of the things that seems under-recognized in all the talk about E Coli is that it is pervasive among humans. First of all, it resides peacefully in your intestines where it helps you digest your food. Without it, you would die.
Of course, since humans, um, go to the loo, and since it's kind of hard to herd bacteria, we get it on our hands, will ye or nill ye. Children, in particular, do. It gets spread everywhere. One of the interesting things (since a previous poster talked about water) demonstrating how easy it is to spread, is this.
I live in a semi-rural area, in which there are a lot of wells serving serious ranches and "hobby farms". Very clean water can be found in abundance not terribly far down. However, if one has a pump fellow do any work on one's well, one has to "shock" the well with chlorine (ordinary bleach) afterward. The reason is that the pump guy's mere handling the pump will cause bacteria (mostly E Coli and Coliform) to get on the pump. The pump goes back into the well and bacteria can then proliferate even in that environment. To cure it, the owner pours a gallon or two of bleach down the well, lets it sit for a couple of hours, then runs all the water outlets until he can no longer smell the chlorine smell. If the well is properly sealed, that does it.
Just touching the pump. That's all it takes.
Now, there is a belief; doubtless true, that there are these more virulent strains that are much more harmful than the E Coli your child has on his hands every day. Some believe those strains develop due to grain feeding of animals, and have their theories about that. But it's also true (as a German study demonstrated) that farm-raised kids who are exposed to the bovine forms of E Coli pervasively, never get those virulent strains that pop up from time to time in, e.g., hamburger or, (as we saw two years ago) vegetables. For whatever reason, children who are exposed might get a bit sick (just one of those childhood things) and throw up, are less reactive than people who acquire it as adults or teens. (Rather like Polio which affects one worse the older one is when one gets it.)
So, it's possible that the occasional outbreaks of serious E Coli we see now and then, are due more to our urban lifestyles than to how our food is prepared. Men (particularly Indo-Europeans) have lived with cattle for thousands of years. We spent thousands of years herding on the Eurasian plain before we ever built a city or raised crops. It may be taken as instructive that Indo-Europeans are virtually unique in retaining lactose tolerance into adulthood. Other peoples don't.
Ironically, it may be our (historically recent) divorce from the proximity to cattle (and other herd animals, perhaps) that has made us more vulnerable to things for which we "bought" immunity or tolerance through the millenia.
And yes, as a father I deliberately took my young children into the corrals so they would be exposed to cattle bacteria. Possibly they threw up a few times or got diarrhea for a day or a mild fever one night because of it. Children get such things all the time anyway, and we never know from where. Now, I take my grandchildren down to play in the corrals, and for the same reason. After all, if they have inborn potential due to perhaps hundreds of thousands of years of genetic acquisition, to be immune to cattle vector diseases (and there are more of them than E Coli, and they exist in the cities too) why waste it?