Chance of HIV infection?

On Penn and Teller鈥檚 BS, I believe they said once that if you sleep with a person infected with HIV, you only have 1/500 chance of getting HIV. From health class I had the impression that there is a 100% chance of infection if you sleep with an infected person.

P&T鈥檚 BS is definitely biased鈥攖hey don鈥檛 lie, but they present only 鈥渢heir鈥?side of the evidence. So here鈥檚 what I wonder: since it is a show aimed mostly at men, they meant that men have a 1/500 chance if they have intercourse with an infected woman. Since most of the fluid moves from a man into a woman, a woman might actually have a close to 100% chance. Or were they correct for all humans? Does my point have merit at all? Do men have a lower chances of getting HIV than women if they sleep (heterosexually) with infected partners. Does it also mean that homosexual men (those on the receiving end) have a higher chance of infection than their partners? Does it mean that lesbians have a low chance of infecting one another?

Oh, my. HIV infection is transferred when body fluids from one person get into the system of another person. This is NOT just from semen; most common is when small tears occur during sex (which they almost always do, they are just so small we don't feel/notice them), and blood or other fluids such as semen/vaginal secretions transfer through them. Men and women have the same chance of getting HIV, all other factors being equal. Gay men, currently, have a higher chance simply because there are more gay men that have HIV than straight men. Lesbians can get HIV also, from fluids transfered during sex, just like everyone else. Oral sex can transfer saliva and blood both, and during oral sex you get exposed to either vaginal fluid, blood, or semen. The reason why you don't have a 100% chance is because there is the chance that the fluid you pass won't have the virus in it, or the odd chance the fluid might not get to a membrane it can pass through. Infection is spread by chain, in which you must have 3 elements: a source, a host, and a method of transmission. NOTHING has a 100% chance of spreading. I don't know about the 1/500. All I know for sure is, abstinence decreases your chances greatly since it isn't as easy to get from kissing/fondling, and using a condom/dental dam also makes a very large difference in your odds. And, there are other, more common things to catch out there that these help protect you from, like Hepatitis and Herpes. Be careful out there!

I don't believe the 1/500 part is accurate. There are quite a few people with AIDS today. If it was a 1/500 chance, AIDS would've died out by now.

no, its not a 1/500 chance, for that they meant it by casual contact, not from intercourse or in a health care situation.
It is very difficult for AIDS to live outside an infected host (will ide within minutes), also, for you to become truely infected, a large amount of the virus must be passed into your body.
For intercouse, it is not a 100% chance of transmittance, but it is higher than 50%.

Women have a greater chance of becoming infected. NO glove = NO love.