Puzzled about some data

Hi, I'm new to this HIV forum and I'm actually quite surprised from the data I get from this forum that HIV transmission through sexual activities is much more difficult than what the general public had thought. I read that the chance of getting HIV infected through unprotected vaginal sex with a HIV positive person in a single occasion is 1 in 1000. Imagine how slim the chance is even if it is 1 in 100. I'm not trying to challenge the validity of these data from the doctors here but I'm just puzzled that if the chance is so slim how come HIV can become an epidemic with so many people infected around the world? Maybe most of the cases are not through casual sex? Hope someone can enlighten me on this.

[chicjing]

And imagine even in countries like thailand where HIV prevalence is as high as 1.5%, with a chance of 1 in 1000 for every single unprotected vaginal intercourse, how much can the chance be for a person to catch HIV by sleeping  around and perform unprotected sex all year through before he met that 'someone' from the 1.5% population and actually get infected through the 1 in 1000 chance.

And transmissionof HIV through unprotected oral sex is virtually zero? Does this mean we don't have to worry about oral sex at all.

I'm really puzzled. Pls help.

[ExtremelyWorried21]

Those statistics are widely known in the medical community if you search through reputable websites.
They are based on years of research. It's impossible to put a statistic on each single individual encounter, but they give us a very good idea of the chances.

The reason HIV is so widespread in places like Africa is thought to be because of the prevalence of other STD's especially ulcerative (Herpes, Syphilis) as well as other co-factors such as multiple partners, dry sex, viral load, etc.

The media does a good job at exaggerating the risks and rates of infections, which causes a lot of worry and panic.

There are different statistics to different acts of sex.
It

[ExtremelyWorried21]

BTW, that 1/1000 to 1/2000 statistic would be for a man who had sex with a KNOWN infected woman.

Taking into account the fact that we don't know who would be infected, the real stats would be much greater (i.e. 1/10,000).

That DOES NOT mean that you can carry on having unprotected sex with random people. The stats above do not cater for the co-factors such as viral load. Remember, there is a possibility for transmission on the first time.

[chicjing]

Did anyone remember the HIV outbreak in the porn industry in 2004, where Darren James had transmitted the virus to three other pornstars in one month time. If the transmission rate is that low even for unprotected sex, how would it be spreaded out so quickly in one month time? Is it possible that they are involved in other activities like anal sex or double penetration where the risk factor is much much higher?

[ExtremelyWorried21]

Not that I would know myself of course! But if you notice, porn scene's typically are very prolonged, probably even more than what you see because of different takes etc.

They also involve a number of different sexual acts, most incorporating them all (anal, vaginal, oral, etc.).

Also if he was recently infected there would have been a higher chance of transmission anyway.
There was an example of this in a story before: A porn star had gone to shoot a movie in Brazil I believe, had sex with multiple women where he was infected, then immediately went back to the US to shoot more movies within a short space of time.

[chicjing]

1/10,000 chance is something like getting strike by lightning when we walk out of the street? If people do not worry about getting struck by lightning when walking out on a street, why should they worry about catching HIV by having unprotected sex with anyone?

Sorry I'm not trying to make an argument or challenging anything, I just want to know that if my understanding of these statistics are correct. I know probability is just a number denoting how likely the event is going to happen. Regardless of what the probability is if it happens it is one, if it doesn't it is zero. I think there would be plenty of people reading this forum and thinking of the same thing as I do. It is necessary to make it clear what we are understanding here.

[amaravatiboy]

chicjing,
The figure 1/1000 is a probability figure.
To start with the probability figure is 1 in 1000 exposures...(this assumes that 1 person is infected and others not)
Now after the first infection ..there would be 2 people infected so the cummilative probability would be 2/1000......still low!!
...this would continue to remain remain low initially..but after a while. the cumulative probability value would start getting into the "not so low" region.

remember each new infection reduces the cumulative probability value...

also, if you follow the adis infection graph...it was initially low.. only after many years did it rise..thats because NOW there are many many more HIV+ people having unprotectd sex..

[monkeyflower]

Extremelyworried21 has exactly the right perspective and information.

Cultural beliefs also factor in transmission. For instance, in many areas it is believed that the cure for HIV is intercourse with virgins, so you have HIV infected guys raping young children and babies.

[monkeyflower]

amaravatiboy's interpretation of the statistics is incorrect. There is a statistical risk of 1 in 2000 PER ACT for unprotected vaginal intercourse, not overall. Likewise, there is a 1 in 10,000 chance PER ACT for blowjobs.

[ExtremelyWorried21]

It's VERY irresponsible to assume that you can go about having unprotected sex with random women based on those statistics.
Like I said, there are various other factors to consider here. Plus various other STD's that are much easier to catch like, for example... Herpes.

There is a chance that you could become infected on the first encounter, why would you want to take that risk?

You CANNOT play the chance game with this, is it really worth risking the rest of your life for one night of unprotected sex??? That

[chicjing]

1/1000 is the probability of getting infected through unprotected vaginal sex in one single occasion with a KNOWN HIV POSITIVE CARRIER. Not that 1 in every 1000 people is HIV positive initially, and accumulate the HIV positive population exponentially through infection. This will be what is called 'prevalence rate' if I understand your interpretation correctly. Anyway the prevalence rate of HIV in some mediumly prevalent countries like Thailand is something like 1.5%, much higher than 1 in 1000.

[ExtremelyWorried21]

My last post was in reply to the last rather silly question from chicjing.

Sorry Monkeyflower, didn't want to look like that was an attack on you!

[chicjing]

The reason I'm asking this question is I have an unprotected sexual encounter with a prostitute in Thailand some two years ago. This is the only unprotected sex that I've ever had up to this point in my life. I was with her for about 4 days and there were three unprotected vaginal intercourse. This had been the most regretful thing that I had ever done. I was burdened with this encounter for two years before I took the courage to go for a HIV test. Now that the result will be out within a few days I'm worried as hell. These few days pass like years for me.

But after tumbling into this site and read all the comments by these professional doctors here, it seems that I have nothing to worry about as the chance of getting infected through just one unprotected sex is something almost like zero, that I would have to be REALLY unlucky to get infected. I would be happy if I'm right about this and this would make the next few days easier for me.

[amaravatiboy]

Please remember Its a probability figure for ONE unprotected encounter.
The point here is not in the probability value...it could be anything (1/1000,1/10000 etc).
It's how you arrive at such probability values. Probability is never calculated on per act basis.
Its always done on a larger data.
for eg: if 1000 hiv+ people have sex say 100 times a year. and this results in 100 new infection.. we get a probability figure of 1/1000.

Now we say that the probability of getting hiv is 1 in 1000.. but again we need to remember Its a PROBABILITY figure.
you could as well get infected in the first encounter as well.

[Teak]

Chances or not, if one is not in a monogamist relationship and has unprotected sex chances are irrelevant, YOU TEST.

[ExtremelyWorried21]

My apologies. I thought you we're actually planning on having unsafe sex based on the figures.

If I were you, I'd post your full story about the sex worker to Dr HHH. I'm not 100% about the prevalence of HIV in that area.

The odds are very much with you either way. Good luck  

[chicjing]

I agree with you that we cannot take the chance game. What I'm trying to do is to grasp a more realistic picture of what these statistics mean. 1/1000 is an extremely rare chance, just roll three dices and try to get three 6s in a row, and experience how rare 1/216 is. I'm really in doubt if this 1/1000 is realistic, would there still be so many people getting infected with HIV simply through unprotected vaginal intercourse.

[monkeyflower]

No. The statistics we quoted are not calculated that way. They are per act, with a known infected person.

Scroll down to table 1.  http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5402a1.htm

[scared indian]

whewwww  a good answer in last ,,nice one

[monkeyflower]

Reread extremelyworried21's response for some of the reasons why unprotected vaginal intercourse can be such a significant transmission route in many areas. Dry sex=trauma. Raping young children=trauma. Uncircumcised penises have been shown to be a factor. And general sexual behavior is also a factor.

[chicjing]

"if 1000 hiv+ people have sex say 100 times a year. and this results in 100 new infection.. we get a probability figure of 1/1000."

Well I guess you mean each of these 1000 HIV+ people have 100 times sex in one year, that is a total of 100,000 sexual activities involving a HIV+ people, and that results in another 100 new infections, so the calculation goes like this:

(100 new infection)/(1000 hiv+ people) (100 times sex) = 1/1000

I understand what you mean.

[monkeyflower]

NO. Amaravatiboy is WRONG. That is not how they are calculated. Read the link I posted from the CDC. They are PER ACT.

[ExtremelyWorried21]

Monkeyflower is right. Good article too, worth a read

[Confused about HIV risk]

I think Mark Twain said:

'There are lies, damn lies, and statistics.'

The problem with statistics and probability is that they are a guide, but they mean nothing when your number is called.  If people went their whole lives based on statistics, nobody would ever play the lottery.  The problem with life is there is extreme good luck and extreme bad luck.  And I have no idea why that is.

[Confused about HIV risk]

Even in physics, once thought to eventually solve all mankind and the history and mysteries of the universe, now at it's fundametal level has the 'Heisenberg Uncertainty Principle' right up there with Einstein's relativity.  Good luck eveyone trying to find answers in science.

The only thing an individual knows for sure is that somehow, someway, sometime he or she is going to die.  But I'm sure that it's even theoretically possible to be immortal in accordance with quantum mechanics and sub-atomic physics.  It may be a 1 in a 100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 chance of being immortal.  Since it already happened to Jesus, I don't think it's going to happen again.

[chicjing]

The statistics posted in Table 1 of your link is referring to unprotected sex right? I read the title of the link is talking about 'in the United States'. I also read a few articles that they specifically state 'in the United States'. But I guess this is a purely biological issue and the probability should be the same in whatever country right?

[amaravatiboy]

My Friend,
My comment was with regard to "how one would calculate estimated risk per act prbability".

I did not intend to contest on the authenticity of  the figures given in "Table 1" CDC.

[peekawho]

What the heck does it matter???  The message is, use a condom for vaginal or anal sex, and get tested every year  if you are not in a mutually committed relationship.  Don't share needles.  Always ask your partners status prior to sex.  

If you do that, you shouldn't have a lot to worry about.

[chicjing]

Im worried that the 1/1000 statistics is going to mislead some people into thinking that unsafe sex is not really that unsafe.. there is a need to clarify what this number means.

Lets say there are 1000 people in a lucky draw, one of them will get a grand prize. Statistic tells us that each one will only have 1/1000 chance of getting the grand prize. But ultimately one person WILL get that grand prize even the probability to him is 1/1000 same as everyone else. With the same probability, 10 people will get the grand prize when there are 10,000 participants, 100 people when there are 100,000 participants, and 1000 people when there are  1 million participants! Even to all these grand prize winners their probability of winning is 1/1000.

The only way to not to get that grand prize is not to join the lucky draw at all. i.e. don't engage in any unsafe sex act!

[monkeyflower]

Trust me. You aren't going to get any disagreement on this board.

The problem is that on these boards, people have such an inaccurate perception of the risks around sex that they become incapable of having happy, relaxed, fulfilling sexual relationships. Instead, every sexual contact (regardless of safety) is fraught with anxiety and misery, followed by weeks of intense angst and obsession with all things HIV/STD. It's sad.