Well the way it works in the comics is that everyone is infected but it only activates when you die, so even if you just get shot to death you still turn. I think in Guts the "don't get any on your skin" thing was just them being overly cautious because it's not like zombie blood on you would kill you unless it got in your eyes, nose, ears or mouth. Then again, the "skin" thing seems to come up for a lot of people as a complaint against the show, so I think I'm in the minority on not really caring about that particular point.