I have very worried friend who thinks he might get AIDS.His story is that about 18 months ago,he took a bath in a bath tub and masturbated under water.He is afraid that if someone,HIV positive who had been in the hotel room had masturbated a few minutes ago or left some blood or semen in the bathtub,it might have mixed with the water and entered in his penis when he was masturbating.Until now, no symptoms of AIDS have appeared.He is very worried about being at risk of AIDS.Does he pose a risk,if any of getting AIDS?