I understand your fear hun, same thing happened to me a few years ago. It was xmas eve, and me and my then bf were coming back from a pub in edinburgh. I saw a young guy lying on the pavement, so I insisted we had a closer look, and it turned out he had smashed his head on the pavement and was bleeding profusely. So I kneeled down and pressed my cardigan (that I took off even if it was freezing cold! lol) against his head wound and held his hand while my bf went to call an ambulance. I ended up with blood all over me, and on my hands. I made sure I had a test 3 months later, jus in case, but it was unlikely to be positive anyway. I'd have had to be bleeding myself for any contamination to happen, provided he even was a carrier!