Whats up with my family?

Okay so a few months ago, my mom had a HUGE pimple like thing on the back of her leg. She went to the hospital and they had to cut open the zit and put gauze inside it. -gross i know- We asked the doc. what it was and he said it was bacteria going into a cut or pore. so we cleaned all tweezers, and basically cleaned the whole house. But NOW my dad has recently had one on his back and now he is getting another on his back. Do you possibly know where these things are coming from? How to prevent them? I mean everytime I get a pimple, Im afraid it will turn into one because they are extremely painfull, so ive heard. Helppp.