Any little scratch can turn bad on you at any time. All it takes is a little glitch of some sort to cause the pathogen to get the upper hand on the immune system. It's so rare that we shouldn't worry about it. If we worry about every little scratch, we are prisoners to our own fear. The ticket is fast reaction if there's unusual tenderness, redness, or swelling in the wound. That's when you should start worrying, and get it looked at immediately.