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transmission risk (HIV STATISTICS)

May 1, 2007

Dear Dr. Bob,

Just over 3 weeks ago, I did something extremely out of character for which I shall always be ashamed. On a bachelor party, I visited a strip club/brothel and whilst extremely intoxicated over the course of several hours and despite being happily married, I had insertive oral+vaginal intercourse with 3 strippers of unknown status I don't know what the hell I was thinking. My recollection is that all acts were protected start to finish and despite my drunken state, I'm pretty sure I would have remembered if there had been any slippage or breakage of the condoms or penetration/fellatio without protection. Nevertheless, since that evening I have become extremely worried about the prospect of having become HIV+ (not to mention having taken a good long look at my alcohol consumption habits).

On searching the Internet, and despite a sex education which wasn't based on the abstinence school of prevention, I was surprised at how little I actually knew about STI transmission, both from the standpoint of catching STIs (such as HSV) whilst wearing a condom, but also for the relatively low risks for transmission of HIV from unprotected sex acts.

As far as I can make out from my research, the 'per-act' estimated risk figures by category you quote on this forum are the those numbers which were derived from various studies, and are those used by the CDC (and were significantly lower that the ~100% figure I had heard during sex-ed, albeit that this was in the early 90s).

I assume that these numbers represent statistical averages derived by HIV/AIDS reporting, and also epidemilogical (is that the right word?) models, but I wondered if separate models exist to estimate how much the risk is modified (i.e., variance) as a function of length of exposure / viral load of serpositive partner etc.

Anyway, whether you answer my question or not, thanks to your tireless work on this forum, I've now got a reasonable idea of my level of risk (virtually non-existent, on paper at least), have already booked in for a definitive test at the 3 month mark and have been to the clinic for a STI check.

However, I do not expect the remainder of my window period (9 weeks) to be easy. Although I totally respect and admire your belief in being entirely open with your partner, after thinking long and hard I have decided not to do so. I would hope not to be judged as an evil person because of this, suffice to say that the consequences of doing so would reach far further than those immediately surrounding me.

Hopefully due to the stress of this situation, my very real disgust with my isolated actions, and nothing more severe like ARS, I have a constant sore throat, fatigue and night sweats (despite not actually having a fever, according to my thermometer). I am trying to remain as upbeat as possible that these symptoms are nothing to worry about and am one of the worried well.

Having written all this (mainly as a form of therapy!), I feel I have to join so many others in letting you know that you are the most compassionate, inspirational human being I have had the fortune of encountering for a long, long time. If everyone had as much passion and commitment as you do, the world would not only be a better place, but a place without the pain and agony that HIV/AIDS brings.

Finally, as soon as I am able I would be honored to make a donation to your foundation. For the reasons mentioned above, I would like to do this as anonymously as possible, could you please advise the best way to do this?

Response from Dr. Frascino


You are correct on many aspects of your post. The statistical estimates of risk per-act for various sexual activities are indeed generated from epidemiological studies. These statistical risk estimates give some general idea of level of risk, particularly in comparison to other activities. For any one individual situation, there are many variables involved, including both host factors (immune integrity, age, concurrent infections, etc.) and viral factors (viral strain, viral load, etc.). It would be statistically impossible to factor all these potential variables into an actual specific risk calculation for an unprotected sexual exposure. (See below.)

You are also correct that your specific risk would be "virtually nonexistent" if you were indeed "protected start to finish" with your trio of strippers. That's assuming the latex condoms were used properly and did not fail.

Your "symptoms" are very nonspecific and not worrisome for HIV ARS (acute retroviral syndrome).

I agree: Because you are worried, you should have an HIV-screening test at the three-month mark to definitively put your fears to rest.

Regarding leveling with your wife, that's a personal decision. In general I encourage honesty as the best way to confront and cope with the guilt associated with such indiscretions.

Finally, I should mention you shouldn't be too hard on yourself. We are all human, which means we all make mistakes. Yes, even yours truly. In fact, if you knew some of mine, they would curl your. That's assuming you don't already have a set of locks like Shirley Temple. The important thing is that we admit our indiscretions, accept the consequences of our actions and learn from our mistakes. It appears you are doing just that.

Thank you for your donation to The Robert James Frascino AIDS Foundation. If you want it to remain anonymous, you can just include a note to that effect with your gift and we'll make sure you do not receive any acknowledgement or thank-you letters. Alternatively, you can send a money order or cash if you don't want to use your credit card or personal check.

The Foundation's address is:

The Robert James Frascino AIDS Foundation 1000 Fremont Ave., Suite 145 Los Altos, CA 94024

In return I'm sending you my best good-luck/good-health karma that your three-month definitive test is negative, as I very strongly believe it will indeed be!

Good luck.

Dr. Bob

It's hard to believe your statistics!! (HIV STATISTICS) Apr 23, 2007

Hey Dr. Bob, I first read your site about 3 years ago when I was a sophmore in college and worried about a high risk HIV exposure (turned out negative). Today, I am a first year medical student and hope to eventually make half the impact you do on peoples' lives. I do have a question for you though. Often times you'll quote a risk being 1-4 in 10,000 or .5 in 10000 or something like that. To some that may sound equivilant to the probability of getting hit by a bolt of lightening while holding hands with a left handed lithuanian. How can it be true that engaging in unprotected vaginal intercourse with someone known to be HIV positive carries such a low risk that statistically you must have sex 10,000 times before you may EXPECT to become infected. Most happily married couples who have crazy mad grab-the-sheets sex don't do it 10,000 times over their entire lives!

Response from Dr. Frascino

Hi Med. Stud.,

Welcome back to the forum. Chances are as a first-year medical student you'll be learning a great deal about statistics and how to appropriately interpret them in a medical context. In general I would prefer not to give a specific number when explaining HIV risk, as this can indeed be very misleading to those who don't understand the limitations of statistical-risk estimates and attempt to apply these statistics in absolute terms to their individual situations. It's important to point out HIV transmission involves many variables other than just "route of exposure" statistical risk estimates. Factors, such as viral load, viral strain, host immune integrity and concurrent infections, as well as a variety of other factors, come into play for any specific situation. That is why I try to impress on folks these statistics are mere estimates. They provide information about general risk levels for various sexual activities, but should not be considered the absolute total and exact risks applicable to their specific situations. There are far too many variables (viral factors, host factors, situational factors, etc.) to accurately compute those numbers.

Statistics are not always easy to comprehend. For instance, when you flip a coin, the chance it comes up heads is one in two, right? Some folks could infer from that statistical chance that if they flip the coin twice it will come up heads at least once. This is obviously not true. In fact, even if you flipped the coin and it came up tails 10 times in a row, the chance your next flip will come up heads remains exactly the same as the first flip, one in two. The chance of coming up heads doesn't increase because you just flipped a bunch of tails. Similarly, with the HIV statistical-risk estimates of, say, 1 in 10,000, that doesn't mean you can perform that particular sex act 9,999 times before you have to worry about contracting the virus.

I should also point out the statistics I quote are really not "my" statistics, but those published by the CDC (Centers for Disease Control). They are estimated per-act statistical risks for acquiring HIV, based on the epidemiological studies published in the medical literature. Their purpose is to give some idea of relative risk of various sexual exposures. So if unprotected receptive oral sex with a poz partner carries a 1-in-10,000-exposures estimated statistical risk and unprotected receptive vaginal sex with a poz partner carries a 10-per-10,000 exposure risk, the important fact is that it's about 10 times more risky to have unprotected vaginal sex compared to oral sex. Similarly, the statistics would indicate it's 50 times more risky to have unprotected receptive anal sex and 9,000 times more risky to get a blood transfusion with HIV-tainted blood. However, the WWWs (Worldwide Worried Wells) are often not at all satisfied with "relative risk" figures. They want their specific risk, which as I mentioned above is nearly impossible to accurately calculate due to the number of variables involved. Also is a group of folks who are so irrationally worried about becoming infected they almost seem to fear they can catch HIV in the mail. In general HIV is much more difficult to acquire than most people think. Most folks are shocked to realize that even an exposure like mine, where I was stuck by an HIV-contaminated needle, carries a risk of only 1 in 300! Again this may seem like a low number just like the seemingly low numbers for various types of sexual risks.

And so we are left with three take-home messages:

1. HIV can occur even with a single exposure, even if the estimated statistical risk seems low. There are 45,000,000 of us who can attest to that fact.

2. Different sexual activities carry different levels of relative risk for contracting HIV. Unprotected receptive anal sex carries the highest risk.

3. HIV is probably not as easy to acquire as many people fear. Over twenty-five years of epidemiologic statistical research have provided us with consistent data related to these relative risks.

These messages can sometimes be difficult for folks to understand, because they are not intuitively obvious and may even seem contradictory. However, in reality, they are not. It's all in the interpretation and understanding of facts in the context of "crazy mad grasp-the-sheets sex."

Dr. Bob

comment on : It's hard to believe your statistics!! (HIV STATISTICS) Apr 25, 2007

If the probability of being infected in a single exposure is p = 1/1000, the probability of being infected in n exposures is given by the binomial: P(n) = 1 - (1-p)^n in our case, if n where 1000, the probability of being infected in 1000 exposures is aprox 63% ( P(1000) = 0.6323) Having sex 3 times a week aprox, means that more than 1/2 of the magnetic couples were become infected before 6 years, only having vaginal unprotected sex. Statistics aplyies only to a great number of people or a great number of exposures. ** hugs ** and sory about my english.

Response from Dr. Frascino


Your English is quite understandable. It's statistics that tend to confuse folks! I absolutely agree statistics apply to large numbers of people.

Dr. Bob

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