Heterosexual HIV Risk

[mcy5304]

Dr. Handsfield,

I'm puzzled over something I'm not being able to find (mostly on the internet): a single example of a woman transmitting HIV to a man via purely (heterosexual) vaginal intercourse, i.e., without other risk factors such as common IV drug use.  Instead, what I've found is a collection of studies (almost none in the U.S.) that seem to suggest just the opposite.  In particular, the 1997 Padian study found that only 2 out of 82 HIV- men contracted HIV from their positive partners over a roughly 10-year period.  Besides there being almost no statistical power in such a small sampled test, would you be surprised to find one or two guys out of 82 that lied about another risk factor?

My question: in your professional opinion, how likely is it that HIV is *only* transmitted through either receptive anal sex or through mixing blood, e.g., sharing needles/transfusions?  Accounting for the fact that a substantial fraction of women engage in anal intercourse, and the likelihood that many "straight" men also do so but lie about it, doesn't this hypothesis better explain the data?  Wouldn't even a "very small" chance of transmission generate far more substantiated heterosexual woman-to-man cases than we see?

Perhaps you have seen such a case(s?) in your professional experience, but I haven't been able to find a single example or testimonial that suggested that man-to-woman sexual transmission is even possible.  Thank you very much in advance.



  

    

[H. Hunter Handsfield, M.D.]

Thanks for an interesting and intellectually stimulating infection.

Millions of men worldwide have been infected through vaginal intercourse; there is no doubt it is a real risk factor, indeed the primary route of tranmission of HIV to men outside industrialized countries.  Further, I have no doubt that some heterosexual HIV transmissions from female to male occur after single episodes of vaginal sex.  That said, the risk in industrialized countries for any single episode of vaginal sex is low, which is why the data also support my reassuring comments to men who post questions on this forum about single episodes of exposure.

The reasons for the differences between industrialized countries and developing ones has to do with a variety of cofactors that operate as multipliers of transmission efficiency:  the proportion of men in the population who are not circumcised, the prevalence of HSV-2, the frequency of other STDs, availability of antiretroviral therapy, the proportion of the populations with multiple or concurrent partners (higher in sub-Saharan Africa than in the US, for example), and stage of the epidemic (which translates into the average viral load in infected persons). By itself, each of those factors probably accounts for only a small part of the difference, but in combination, they make all the difference.  The rarity of documentation of female to male transmission by vaginal sex in the US does not imply that anal sex is the main route of infection; perhaps that has some minor influence, but the other factors I mention are generally believed to be far more important.

Regards--  HHH, MD

[mcy5304]

For example, on the health department websites for Austin and Houston (I live in Texas), the cases of heterosexual transmission for men appear almost non-existent.  Each site breaks it down by race (I'm sure the Seattle health department does the same thing), and for white men, the fraction living with HIV/AIDS in Austin and Houston are 1% and 2% respectively.  Even if the true heterosexual risk to men were 0 (which I'm asking about, not claiming), you would certainly expect some people to lie about their risk factors, especially given the social costs of admitting homosexuality or IV drug use.

[Confused about HIV risk]

Do you live in Austin or Houston?  I live in Houston, moved here a year ago.  I posed maybe a similar/ related question to Dr. H. on this forum on Feb. 23rd because, being straight, I was wondering what my chances really are of being infected by annonymous women I know nothing about, except that they're promiscuous.  You might want to read it.

[scarycat]

Thanks for doing the research. Part of me truly want to believe that HIV can not be transmitted from Women to Men through vaginal sex. But the fact is, we may never know for sure. So where does that leave us with how to protect ourselves from HIV for practical purposes? Back to wearing condoms.

[H. Hunter Handsfield, M.D.]

Of course my opening line is supposed to say thanks for an interesting and intellectually stimulating question, not infection....

HHH, MD

[Confused about HIV risk]

I just went to the statistics page for Houston for the Texas Department of Public Health.  Of the 726 men who were infected in 2005, only 59 were from heterosexual exposure, that accounts to 8.1%.  That compares with 60% claiming gay exposure.  Very interesting since the vast majority of the population is heterosexual.  

I've read numerous reports on the issue, and having suffered from an over-inflated anxiety about the issue most of my life, it still seems still the vast majority of new infections, for men in the U.S., come from gay sex and drug use.  Not to say don't wear a rubber while having vaginal, but don't be afraid to have vaginal while wearing a rubber.

One report, I can't remember which one, attributed 25% of the new infections in the U.S. to the phenomonon of 'bug chasing', gay men deliberately trying to become infected.  Read an article on it - very disturbing.  The negative gays trying to become infected are called 'bug chasers' and the positive gays willing to infect are called 'gift givers'.  They use terms like 'being bred' and things like that.  Really disturbing stuff.

[Confused about HIV risk]

Here's that article.

http://www.rollingstone.com/news/story/5939950/bug_chasers

[mcy5304]

Dr. Handsfield,

Thanks very much for your thoughtful reply -- that response was exactly of the type I was hoping to get.  I hadn't considered the importance of the other cofactors you mention, but understand how they would likely influence the vaginal transmissibility of HIV.

I'm double dipping a bit, and if you ignore this question, I completely understand.  Have you, in your 30+ years as a practicing clinical physician, happened upon a case in which a heterosexual, non-IV drug using man unambiguously acquired HIV from vaginal sex (even repeated exposure)?  I'm just curious, and not in any way challenging your belief that millions of men have been infected via vaginal intercourse.  With regard to medical matters, your training and experience is several orders of magnitude more than mine will ever be, and I accept your words as truth.

Thank you -- I will not post any more questions in this thread.

  










  

[mcy5304]

I was specifically referring to white males in Houston and Austin.  I'm looking at the numbers right now.  From 1981-12/31/2006, Houston has recorded 23,957 AIDS cases.  Of these, 9,907 have been white males.  Of white males, only 194 were heterosexual cases.  In 25 years.  

In Austin (where I live), there have been 14 such cases, out of about 3,500 cummulative AIDS cases.  In 24 years.

My original question to Dr. Handsfield was motivated by this observation.  My intuition was that heterosexual transmission from women to men doesn't really happen, or if it does, is *extremely* rare.  Dr. Handsfield mentioned that such cases are rare in the states (and other industrialized countries), but that it is largely due to the absence of other complicating factors.  

[H. Hunter Handsfield, M.D.]

I have seen plenty of HIV infected men whose only exposures were vaginal sex, but only after multiple exposures--i.e. the regular partners of infected women.  But never in someone who had only a single high risk exposure.

Persons with anxiety-driven concerns based on misunderstanding of the real risks:  take it to the HIV support forum if you want non-professional advice.  This forum is reserved for more serious inquiries.

HHH, MD

[H. Hunter Handsfield, M.D.]

"Part of me truly want to believe that HIV can not be transmitted from Women to Men through vaginal sex. But the fact is, we may never know for sure. So where does that leave us with how to protect ourselves from HIV for practical purposes? Back to wearing condoms."

Using condoms for casual sex?  Well, duh.  Oh, the horror, the horror.

HHH, MD