K.H.
We have a lot of experience with this topic in my household:
My husband was going to a gym quite a bit back in 2007 and he got it. It was on his leg and it was treated (they drained it, packed it, etc...). Seven months later, i got it (I was also going to the same gym). It was scary!! They treated mine and I got over it and never had another issue with it. I felt the same way you do, "how did this happen? We are clean people!" All those feelings are normal.
However, to answer your questions, our doctor told us everyone has it on their skin, but it gets into your system when there is a cut on your skin. Even a tiny one. It's basically beyond your control. Also once you have it, you're more suseptable (sp?) to getting it again. That said, my husband got it again this past January. This time he wound up in the ER. It just wasn't going away with the standard treatment. He spiked a fever and it got really high, so, off we went to the hospital. While there, he had to get antibiotics thru an IV. All is well now.
As far as how it spreads, it's only through direct contact with that person's sore. Kissing has nothing to do with it. As long as you have the sore covered, everyone else will be fine. If you're worried about your 2 year old getting it, my doctor had me give my kids a bleach bath every day to ward off the potential to get it. It's 1 tbsp for every gallon of water. Also, use a lot of Lysol!
It's a little scary wondering if and when one of us will get it again. Anyway, that's our experience with it. Hope this helps!