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Tranmission Mechanisms

Dear Doc. H.

I hope that this post is acceptable as it isn't a 'symptom checker' or a query on a specific case but rather a more general query about HIV transmission mechanisms.  

You have mentioned that you have never seen a male infected by a single heterosexual exposure to vaginal sex, yet have seen plenty of guys infected from multiple exposures to an infected partner.

My question is as to which of two hypotheses explain this:-

1 Multiple exposures carry a higher risk as they are just that, multiple exposures each carrying the same low level of risk.  (ie if someone buys a lottery ticket this weekend, they may have a 1:1,000,000 chance of willing, but if they buy 100 different tickets then their chances are 100 times greater).

2 The risk becomes cumulative, ie gradual exposure to the virus means that a small amount is transferred on multiple occasions, initially insufficient to lead to infection but eventually in sufficient quantity to lead to infection of the male partner.  (ie.  Each subsequent exposure leads to a slightly higher risk of infection than the previous exposure).

You mention that the act of 'fingering' carries virtually no risk of infection, even with small cuts present.  This would seem to suggest that the second is true, as it would be unlikely that this would be an act that would be carried out on repeat occasions, (as cuts heal over time), yet regular unprotected vaginal sex could well be part of an intimate relationship.  Also, is the second hypothesis a more intuitive explanation as to the mass outbreak in Africa, where (in addition to the prevalence of other STDs which enhance transmission) social trends dictate that individuals are perhaps more likely to have multiple concurrent partners.

My final query would be whether or not you are familiar with any documented cases of female to male infection through a single exposure in the absence of major secondary risk factors such as trauma, STDs etc.

3 Responses
239123 tn?1267647614
I have neither the time nor the energy to speculate in detail (again) on the reasons behind the data on HIV transmission risk.  I have done so many times on this forum; you can search the threads (use the search link) to find many other discussions.

In brief, your first scenario clearly is correct, i.e. the risk of catching HIV increases with the number of exposures, that is the risk indeed is cumulative.  The second, that a person becomes more susceptible for each exposure as the number of exposures increases, makes no biologic sense.  The reasons for much higher HIV/AIDS rates in Africa and other places, and among some subpopulations in the US, have to do with stage of epidemic (which reflects the proportion of the population at risk with higher versus lower viral loads), prevalence of other STDs and perhaps other infectious diseases, circumcision status, sexual behavior patterns, and other issues.

I'm sure there are cases of HIV transmission in the circumstances you describe in your closing question.  I'm not aware of any that occurred among my own patients.

You know from my response to your question 2 weeks ago that your negative test result proves you don't have HIV.  Thus, it doesn't matter what the risks were in the exposure events that you were concerned about--which, as I recall, were several years earlier.  Note the forum rule about a maximum of 2 questions ievery 6 months.

Avatar universal
Hey Doc,

Yeah, I'm absolutely and totally satisfied that I, myself am negative.  I fully understand your assurances that a 9 week rapid test is definitive, and as you said, it wasn't so much my last exposure as an expsoure far longer ago that had me worried in the first place.

What's been worrying me is that the 'prompt' for me to test (and to start researcing HIV) was the huge range of Government funded ads, flyers and radio warnings aimed at the 'Ibiza Generation' in the UK (ie young, straight males and females, probably light drug users but not of the injecting variety, who may partake in semi-casual sex).  At the same time needle exchange programmes are closing down, and two good friends of mine who are gay have told me that the warnings of the early to mid nineties aimed at them have almost dried up.

From the stats, it seems that in the UK, (I cant speak for the US), most new infections are indeed heterosexual, but are almost entirely seen in people of African origin, or their UK born partners.  Heterosexual transmission where the infecting partner was themselves infected in Europe make up only 1% of all heterosexual infections.

I guess I'm kind of concerned that our government is targetting the wrong folks in trying to tackle HIV.  I'm certainly not saying that HIV is a 'gay' condition, or a 'IDU' condition, or an 'African' condition, just that with limited funds, maybe we should be targetting the higher risk groups a little more, and the lower risk groups a little less.  

Sorry if I bugged you Doc,  I know your a busy guy, just wondered if you had any thoughts on this..
Avatar universal
I agree Langoustine.
We all need to be careful. But it's interesting that the vast majority of people posting on here are the people statistically least at risk (heterosexual men from Western countries - one-off encounters). It makes you wonder if the health campaigns really are having TOO BIG an impact on the WRONG group.

I'm also a 20-something heterosexual male from the UK, and I really believe that the fear-based advertising in this country, which isn't backed up by the stats, combined with a mild tendency on people's part (including me - common problem) to worry and over analyse things (and believe everything in the media) is creating a huge number of people who are either afraid to have sex, or feel guilty when they do. Just look at the majority of posters on this site for evidence, who become almost suicidal after single episodes of sex.

I myself have lost months worrying about 1 or 2 unprotected encounters (not been able to concentrate on work, constantly surfing for symptoms, 'probabilities' etc). But when I've gone to see the doctor about it, I'm told I don't need testing, stop worrying, extremely low risk, 'almost impossible from one-off' etc (as mirrored by the good doctor's comments on this forum). But the message sent out to heterosexuals in health service campaigns is completely different. Which are we supposed to believe?
If you really analyse the stats as you clearly have done Langoustine, heterosexual HIV transmission in the UK is almost completely limited to a very tiny proportion of people and doesn't really apply to most. Of course, it's everyone's problem, but if you dig a little deeper beneath the generalized "heterosexual HIV explosion in the UK" headlines, the numbers for low-risk UK born people getting HIV are actually very, very low. It's also pretty much impossible to find official, documented evidence of HIV transmission from a low risk female to a low risk male after a one night stand in the UK ANYWHERE (at least on the internet). Yet, that's what most people on here are worried about.
Campaigns in the Western world are based largely on fear (and delivered with the strapline, "heterosexual sex is the fastest growing way to catch HIV"). Rather than focusing on sexual lifestyle and targeting statistically high risk groups, they just hit us with a 'one-size' fits all approach. "HIV is out there waiting to infect us all. Just ONE bad decision or ONE drunken night of passion with a nice girl you met in a bar could well cost you your life."

It's just a shame that heterosexual people who are having nervous breakdowns over HIV have to dig so deep to get to the truth.

The lack of hysteria shown by my own doctors and Dr HHH have actually helped keep me sane when my fears over HIV have been at their highest.

Anyway, that's my two-penny's worth - back to obsessive worrying over HIV!!
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