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# Confusion Over HIV Transmission

I'm a little bit confused as to how these figures work out... for example I have read from numerous websites that having unprotected vaginal sex with someone who is HIV positive has a 1/1000~ chance of contraction of the virus. I've also read from many places that if an average blood drawing needle is reused and has HIV present in it, there is only a .3% chance of transmission.

What is it that makes these numbers so low? From what I understood before, ANY amount of blood/genital fluids with HIV transferred to another person is a transmission. So how does for example, a reused needle immediately used on another patient only have a .3% chance of transmission if a small amount of blood is pretty much directly put into the veins?

I know there are probably a lot of factors used to calculate these odds that I'm not aware of but I can't find any solid info anywhere so was just wondering if anyone had some insight.

Thanks
8 Responses
Not every exposure to the virus results in transmission, in fact, most do not. HIV is a fragile virus and many variables have to be just right for transmission to occur. The statistical odds given by the CDC can be used as a tool to determine which acts are most risky.
Refer to table 1 towards the bottom of the following document:
http://www.aegis.org/pubs/mmwr/2005/RR5402-1.html
These are just numbers for reference only. It certainly does not mean that you need to have sex 1999 times with an infected opposite sex partner or do it with 1999 new partners and get the virus in the next episode. Even if it is true, I ask you a question.

There are 2000 glasses filled with highly refreshing and delicious juice, and JUST one, JUST ONE of these glasses is contaminated with a lethal poison, and nobody knows which that glass is. Would anybody dare to pick up the drink?

Dear friends, you do not have to complete those 2000 or 1000 "events" to get the infection. Nobody, infected today got the virus following these statistical numbers. JUST ONE exposure is enough for an effective transmission provided all the conditions are met.

Bottom line is, be smart and play safe, avoid unprotected penetration or keep yourself limited to "no risk" behaviors when involved with someone of unknown status.

Remember, prevention is the only cure for HIV. Do not confuse yourself with numbers and probabilities because HIV has not learned statistical tools and did not attend any business school to learn them.
Ya I definitely understand that. Everyone should always be safe, I am just curious as to how it works. Thanks for the link Miami, I learned some new things but my question still wasn't addressed.. what exactly are the factors? For example, I've seen the popular figure of needle transmission on a million sites (including the CDC). Needle reuse/sharing from an infected partner has a 30% chance of HepC, 3% for HepB and .3% for HIV. What I do not understand is, why are the numbers like this? If a nurse draws blood from Patient A who is HIV+ and then uses the same needle 10 minutes later to draw blood from Patient B who is HIV-, what is it that causes there to be a 99.7% chance that it won't be transmitted, what exactly are the variables?

Obviously the risk of even being in the above situation is astronomically low, but I am just wondering for the gain of knowledge what exactly the variables contributing to these % chances are if anybody knows.
I don't see any point to pursue the knowledge behind these statistic there. There are some people never got infected even having 100+ exposures, while there are also some people got infected from just one time unprotected isex. And there are also all those variables that are hard to measure too (viral load, duration of exposure etc).
You do realize that the 1/2000 (usually for insertive vaginal) or 1/1000 (usually used for receptive vaginal) is only .05% and .1% respectively?

Obviously everyone needs to be responsible.  But all of this fear of how easily HIV is transmitted is just wrong, causes great anxiety, and ruins alot of sex lives unnecessarily.  Too bad since it is meant to be enjoyed, not feared.
Sure, it is meant to be enjoyed,,,, but with certain limits,,, not left right and center. Who stops you doing anything you want, with your life long committed partner? Well if the same behavior is applied with one timers, sex workers and other high risk individuals, risk is yours.

I agree with you, transmission of HIV is not as easy as thought, its effectiveness depends on a number of factors like viral load, amount of infected fluid, sex (females are more prone to pick), health (one with STD, has more chances to get infected), physiology (uncircumcised males are at a relatively high risk) etc etc,

Having said that, may I ask you a question,

1000 glasses filled with highly refreshing and delicious juice. Only one of these glasses is contaminated with a potent and lethal poison, and no one knows which glass is that. Would you still dare to pick the drink ?

Please do not go for these statistical number, these are for reference only. It certainly does not mean that you will not catch HIV until 1999th episode with infected partner. JUST ONE exposure is enough for transmission, if all the conditions are met. Choice is yours, if you want to continue casually.

There is no perfect treatment for HIV exists todate and prevention is the only cure. Be safe, avoid unprotected penetration or limit yourself to "no risk" behaviors when involved with people of unknown status,, That's what the safe sex is all about.
HIV is a difficult virus to "catch" because it takes large amounts of the virus to exposed to special cells buried deep into the skin or in the blood. Simply, one virus is not enough or a person to get infected. The biggest concentration of the virus is in the blood, followed by vaginal fluid/semen, and then breastmilk and trace amounts in saliva.

The odds listed in the CDC are calculated using statistics gathered by large population and take into account sex acts/persons infected, number of new infections/year, polpulation, and so forth. There are other factors that have an affect on the risk of transmission such as viral load, circumcision length of exposure, and so forth which there is no data on. So the best estimates are as follows:
Sharing a needle with HIV infected person: 1:150
Anal receptive intercourse with HIV infected person: 1:200
Anal insertive intercourse with HIV infected person: 1:1500
Receptive vaginal intercourse with HIV infected person: 1:1000
Insertive vaginal intercourse with HIV infected person: 1:2000
Insertive oral sex with HIV infected person: 1:20000
Insertive oral sex with HIV infected person: 1:10000

These risks are estimates, but are pretty accurate as there has been a lot or research conducted and lots of historical data available from around the world. Bottom line, HIV is a hard virus to catch and usually doesn't occur base on a single act (especially heterosexual sex). Infection usually occurs with repeated exposures between an infected and non-infected person.

Hope that helps!

It's your choice if you remain that casual towards HIV's "friendliness" and stay with those numbers. But tell me why most of the doctors advise to get oneself  tested after just one or two events of unprotected sex with someone of unknown status?

Prevention is the only cure, known to mankind as of now, and prevention means "safe sex" either protected or abstinence or limiting to your committed relationship,,, whatever you pick.