Got pricked by a needle placed on a cab.

I sat in a cab. I didn't notice that there was an open hair pin(with a stainless steel needle I guess) below me. It pricked a little on my scrotum. I am not sure whether blood came out or not after pricking as I was unable to see at that location. I checked the pin. It looked fine only. I also got a tetanus injection the next day. But right now I have seen few videos and some articles where it was mentioned how mentally retarded people place pins/needled in public with an intention to speak HIV/other diseases. Now I'm getting a lot worried regarding that if something could get spread because of that. This is giving me a lot of tension. Can someone advise me what I should do? Should I do some testing or get some medicine or consult a doctor?