I had an encounter today, I sat on a wooden chair not knowing that a nail burged out of it, it hit me on my tigh, and it pierced me with a little blood coming out from the wound, It was a waiting room in a public place, after I left i began to wonder if someone else had sat there a minute or two before me and had the same experience, would I have a chance of contracting HIV if the person is POSITIVE, I am worried... Please help..