First, some of my misconceptions:
1. If you have unprotected sex with an AIDs victim, you'll get AIDS about 100% of the time. Turns out that the transfer rate is about 0.0005%, or 1 in 2,000.
2. If you share a drug needle with an infected person, you'll get AIDS. Actual transmission rate is about 1 in 150.
3. A lot of people have AIDS. Actually there are about 275 women in Iowa with AIDS, or approximately 1 in 5,500.
4. If you get a blood transfusion from infected blood you'll get AIDS. Actual chance is 90%, so I had this one basically right.
So it turns out AIDS isn't so easy to get. From these transfer rates and some additional data we can come to some interesting conclusions:
1. If you were to have completely random, unprotected sex with Iowan women, you could go through eleven million of them before you're expected to contract AIDS. Could be more, could be less, but that's our ballpark. To put this another way, you could have sex with every woman in Iowa and still have only a 13.5% chance of contracting HIV.
And another way -- men are capable of reproduction for about 22,000 days during their lifetime (age 15 till they die). An man could have sex with a random woman every day from puberty to death and have a 0.2% chance to contract HIV before he dies. The avg guy is going to sleep with over 1,000 times less women and enjoy an almost non-existent risk.
2. For women, transmission rates are higher, about double. So you can cut the numbers in half for women.
3. Receptive anal sex is very risky. Chances to get HIV after being fucked in the ass by a man with AIDS is 1 in 200, which is still less than sharing needles, I guess, but a pretty good way to get AIDS. Simply find an infected partner and let him rail you in the ass a couple hundred times and you're pozzed. Double the fun if you share needles at the same time.
4. Let's put this in perspective. Say a man has 100 random one night stands during his lifetime and never uses protection. His chances are 1 in 110,000. His chance to be murdered in Iowa is 1 in 833, car accident 1 in 85, and by falling 1 in 143. This relatively promiscuous man shouldn't really even have AIDs death risk on his radar.
Extra special gold star to anyone who can accurately answer this question:
"If a white male in Iowa takes an AIDS test and it show a positive result, what is the probability that he actually has AIDS? Current tests give false positives 0.0004 to 0.0007% of the time. 80% of AIDS victims in Iowa are male and there are about 1365 people in Iowa with AIDS/HIV right now. Of those AIDS victims, about 996 are black, 399 are hispanic, and 66 are white."
Infection rates for chlamydia, gonorrhea and syphilis are all low as well. Estimated risk of infection is 1 in 2,500 (0.04%). All are curable and non-fatal.
Pregnancy risk is about 2-10%.
Infection rates for Iowa:
Chlamydia: male 1/1,900; female 1/460
Gonorrhea: male 1/3,900; female 1/2,600
Syphilis: male 1/33,000; female, 1/500,000
Men with any STD in Iowa: 1 in 1,235 -- 0.08%
Women with any STD in Iowa: 1 in 391 -- 0.26%
Transmission rates are 20% for men and 50% for females for gonorrhea. If we assume 20% and 50% for all three, total risk to contract any STD from random sex is:
Men 1 in 2,470 (0.04%)
Women 1 in 1,955 (0.05%)
Every 5 miles you drive is as likely to kill you as unprotected sex with a stranger, and each commercial plane flight is over 3 times more likely to kill you. I think it's unfortunate that sex has become something so strongly associated with disease and fear.
"My entire adolescence and adult life – as well as the lives of many of my peers – has been overshadowed by the belief in a deadly, sexually transmittable pathogen and the attendant fear of intimacy and lack of trust that belief engenders." --Rebecca V. Culshaw, AIDS researcher.