I am 34 year old female. Several years ago I got intoxicated and had sexual intercourse with a man that I dated as a young teen. Several months later I heard that he is HIV+. I talked to to his family and they told me that he has AIDS. And has had HIV for several years. My question is,....What is the possibility of contracting HIV/AIDS if a woman has unprotected sex with a man one time? I had a test done about 5 1/2 months after the intercourse that came back negative by the way.

The risk of transmission from a male to a female during a single act of vaginal intercourse is 0.1 - 0.3%, or somewhere between 1 and 3 transmissions for every 1000 acts of vaginal intercourse. These are statistics from large studies of individuals who are at different stages in their disease and can be missleading if one interprets these numbers to mean the risk of a single act is very low. For example their are well described instances where a particularly infectious male infected many women who only had one episode of vaginal intercourse. It is very likely that one of the most important predictors of transmission is the viral load of the infected individual. in the case of mother to child transmission we know if a HIV infected pregnant woman has a viral load of greater than 100,000 copies/ml she has a greater than 50% chance of transmitting HIV to her infant, while a HIV infected pregnant woman with a viral load that is undetectable[ less than 500 copies/ml] has a less than 1% chance of transmitting virus to her infant. Your negative HIV test at 51/2 months after your exposure indicates that you were not infected and hopefully will be a strong incentive to practice safe sex[condoms] in the future. JLS.