Actually it's not surprising. Hospitals are amongst the "cleanest" environments, due to necessity. Lots of people with open wounds that infect easily, lots of people with failing or failed immune systems. So they use more antibiotics and cleaning agents than even the most overprotective mother ever could (which, btw, is about the worst thing you can do to your kids, right after the opposite and having them play with infected needles).
Killing off most germs means that you kill off the weakest of the herd. The ones that are easily affected by aggressive cleaning agents. What you do this way is simply building a better home for the ones that survive, because you never kill them ALL. By the very nature of bacteria, it is virtually impossible to kill them off for good. You will even find a few in intensive care, and one is already enough to create a new culture. They multiply FAST.
The ones that survive the aggressive cleaning agents and the whole antibiotic bombardment are the ones that are toughest, strongest and most resistant. And when they get to multiply, you have a strain of supergerms at your hands.
So, in a nutshell, if you want to kill off your family fast, buy some antibiotic cleaning agents today!