Bacterial contamination on meat is widespread, but mainly on the surface of meat. That's why you can eat charbroiled beef rare. Grinding meat spreads the contamination throughout. That's why it's important to cook hamburger to at least 160 degrees F.
Yeah, I was going to lay that all out for any raw meat eating fools that might be reading this but I figured this was just natures way of getting rid of them so why interfere.