Your answer to “What are the odds of getting AIDS from ordinary heterosexual sex?” dated
09-Dec-1988 probably needs updating. I understand that in my county the rate of AID’s infection was approximately 1 in 40.
Your answer that the probability of getting AIDS in heterosexual sex is 5,000,000 seems a little off. Either your estimate needs updating, condoms are far more effective than the manufacture clam or your best guess is about as old as Vatican astrophysics.
I think you need to remove the old information and provide updated answers.
JamesM, which is your county?
In his column, “What are the odds of getting AIDS from ordinary heterosexual sex? (09-Dec-1988)”, Cecil says
I assume your number refers to AIDS infections from all sources including high-risk groups.
I believe Cecil did update this one, didn’t he? Anyway, you gotta know more about the sex before you can ascribe a risk value to it. Is this “ordinary heterosexual sex” with a prostitute? A stranger? An injection drug user? Is it sex with someone who has had a recent negative HIV test? Because sex is only risky if the partner is likely to be infected with HIV.
A more definable question would be, "what are the odds of contracting HIV through heterosexual sex with someone who is HIV+?
The answer is that it’s still quite unlikely, for a single encounter.
There have been a number of cases of married couples where one person discovered he/she was HIV+ and never passed it on to the partner, even though they presumably were having normal, unprotected sex on a regular basis, perhaps for years. (Arthur Ashe and Paul Michael Glaser’s wife come immediately to mind).
Something you’ll never see on the ‘safe sex’ commercials is that your chance of contracting HIV through unprotected sex with a random person is much lower than the chance of contracting HIV through protected sex with someone in a high risk group. Protected Anal Sex with a member from a high risk group is much, much more dangerous.
And the other variation to this is are you a male or female? I am led to believe(Jill, please correct me if this has changed), but AIDS contraction through the penis, without open sores, is rare and probably nil.
So if this still holds true, a man having sex with an HIV+ woman would be quite rare.
Sam Roza
I think the OP also confused the chance of any one person having HIV and the chance of getting HIV from one sexual encounter.
There’s obviously a lower chance of getting HIV than of having it, because people have sex multiple times. (Well, the lucky ones do…)
I think the 1 in 5M is probably a bit high, but then, more people are high risk than you know. Most people aren’t going to admit to a high-risk background, especially if they believe themselves disease free.
I’d guess that if you sleep with a random person in a bar, you’ve probably got about a 1 in 50 thousand chance of getting HIV. Assuming you’re not going for the $5 whore, or the church girl, just a random sampling of reasonable people.
Then, assuming people have sex with 10-30 people in their life on average, and probably 1000 to 2000 sexual encounters during their 20s, that’d mean one in 25-50 people would get AIDS from p-v sex, over a ten year span with a reasonable number of partners.
Other behaviour will of course modify that risk.
As for changing the risk for any single encounter, it depends on what you term as sex. If you mean two minutes of intercourse, then your chances are lower than if you mean 45 minutes of intercourse. If you wash yourself after sex, you’ll be at a lower risk than if you don’t, though I don’t know by how much. Etc. If you like sex rough, you’re more likely to get a friction burn, increasing vulnerability.
Too many variables to address them all.
It’s less likely, but not impossible for a man to contract HIV from an infected woman. Obviously the presence of sores or other STDs increases the risk. There also may be some substrains of the virus - more common in other parts of the world - that are more likely to be spread heterosexually.
I was going to add that Jill. The strain and subtype also matter in transmission since some are better at anal transmission(the type that infects America and Europe mainly) and some are better at Vaginal transmission(HIV-2, which mainly infects Africa).
But you beat me to it! 
Sam
Jill, do you happen to know - is it true that in Thailand there is a strain that is much easier for men to pick up during heterosexual sex? Or is it that these men already probably have multiple STDs and are therefore more vulnerable?
[[I was going to add that Jill. The strain and subtype also matter in transmission since some are better at anal transmission(the type that infects America and Europe mainly) and some are better at Vaginal transmission(HIV-2, which mainly infects Africa).]]
Not HIV II… I’m talking about another substrain of HIV I that is more easily transmissible via heterosexual sex. HIV II is only distantly related to HIV I. I’ve got an article on the substrains around here somewhere. I’ll add more when I find it.
Jill
I just did a little more reading on this topic. The theory that different substrains of HIV-I are transmissible in different ways is still conjecture. There is no actual evidence that this is so, though there are clearly varying patterns in the mode of transmission in different parts of the world. Different strains are found in different regions, but other environmental factors can influence transmission, too. In Thailand, for example, heterosexual transmission is extensive. This country also has a large-scale sex industry and much injection drug use, which could explain the heterosexual spread. In parts of the world where untreated ulcerative genital diseases are common, where males leave home for long periods of time - like truckers - and come in contact with prostitutes (such as parts of Africa), HIV would also spread more readily from female to male and male to female.
-Jill
My wife is a medical researcher, involved in an ongoing project studying heterosexual transmission of HIV. The project a few dozen “discordant” couples, some of whom use protection, and some who don’t. (As an aside, I find it incredible that many established, monogamous couples have chosen to have unprotected sex, despite knowing that one of them is HIV positive, and despite the warnings from the medical researchers in this project.)
Over the course of the study, which is a couple of years, I believe that about 3 couples have “sero-converted,” all of whom were not using protection
To roughly figure the odds, assume they had
– 3 sero-conversions,
– among 20 couples not using protection,
– over 100 weeks, and,
– having sex an average of 3 times a week.
This would give the appro0ximate probability of getting HIV in just one episode with an infected partner at
3/(201003) = 1 in 2000.
You could multiply the 1/2000 by what you think the probability is that your partner is infected to get an approximate value for a particular episode of unprotected sex.
I have to wonder where the OP lives, that the HIV infection rate is 1 in 40. According to How many people have HIV & AIDS? on the CDC website, in the US, “between 650,000 and 900,000 people are living with HIV.” The estimated 2000 US population, according to Statistical Abstract of the United States on the U.S. Census Bureau’s website, is 274,634,000. This gives us a U.S. infection rate of about 1 in 423 to 1 in 305. Also according to the above CDC page, about 33.4 million people are infected with HIV worldwide. I found varying estimates of world population, so let’s make it simple and say 6 billion, which is less than the actual number. That gives us a worldwide infection rate of about 1 in 180. Of course there are places with an infection rate far above average, but i don’t think Cecil is obligated to write to Zimbabwe. And the figures i calculated from include all high-risk groups.
Phantomwise
…never seen by waking eyes…