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satt comments on Quantified Risks of Gay Male Sex - Less Wrong Discussion

33 Post author: pianoforte611 18 August 2014 11:55PM

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Comment author: Azathoth123 23 August 2014 03:19:13AM 1 point [-]

And yet, as you yourself pointed out, (at least in western countries) its prevalence among heterosexuals is much less than its prevalence among homosexuals.

Comment author: satt 24 August 2014 06:16:05AM 5 points [-]

Which is a consequence of HIV being harder to transmit through heterosexual sex. Which does not automatically imply HIV is impossible to transmit through heterosexual sex.

Comment author: Azathoth123 24 August 2014 06:19:43AM 2 points [-]

That still doesn't explain how HIV spread as much as it did in Southern Africa given how hard it is to transmit heterosexually.

Comment author: satt 24 August 2014 06:35:33AM 3 points [-]

Epidemiologists currently reckon that's mainly down to Southern Africans having multiple concurrent partnerships and low male circumcision rates. (Other factors have likely played a role as well, like South Africa's recent bout of officially-sanctioned HIV/AIDS denialism, and the potentially higher transmissivity of the HIV-1 subtype prevailing in Southern Africa.)

Comment author: Azathoth123 25 August 2014 02:13:02AM 2 points [-]

Southern Africans having multiple concurrent partnerships and low male circumcision rates.

Europe has an even lower circumcision rate.

the potentially higher transmissivity of the HIV-1 subtype prevailing in Southern Africa.

When I first herd this theory ~15 years ago it was accompanied by a prediction that the HIV-1 subtype would break into the western heterosexual population real soon now. Since that has failed to happen, I'm dubious about this theory.

Comment author: satt 25 August 2014 01:04:44PM 3 points [-]

Southern Africans having multiple concurrent partnerships and low male circumcision rates.

Europe has an even lower circumcision rate.

Pay attention to the word "and" in what you quoted, it is actually quite important. The Southern African Journal of HIV Medicine article I linked explicitly addressed Europe's lower circumcision rate:

The now conclusive body of epidemiological and biological evidence confirming the strong association between lack of male circumcision and HIV10-15 is increasingly understood to explain much of the roughly fivefold difference in HIV rates between southern and western Africa7,16 [...] However, this key driver does not explain why HIV has spread so much more extensively in southern Africa than in India or in Europe, where circumcision is similarly uncommon. Although sexual cultures do vary from region to region,20 these differences have not been studied in sufficient depth and their significance is not so obvious. [...]

Of increasing interest to epidemiologists is the observation that in Africa men and women often have more than one – typically two or perhaps three – concurrent partnerships that can overlap for months or years. [...] This pattern of concurrent partnerships differs markedly from that of the pattern of serial monogamy more common in the West – i.e. the tendency to have one relatively long-term (a few months or longer) partner after another – or the more ‘one-off’ casual and commercial sexual encounters that occur everywhere.

It is the conjunction of low male circumcision rates and multiple concurrent partnerships which explains HIV's strong showing in Southern Africa.

the potentially higher transmissivity of the HIV-1 subtype prevailing in Southern Africa.

When I first herd this theory ~15 years ago it was accompanied by a prediction that the HIV-1 subtype would break into the western heterosexual population real soon now. Since that has failed to happen, I'm dubious about this theory.

I don't give that point any more weight than the last time you raised it (which I can't link because the relevant post got deleted). Now, as then, you haven't cited any specific person or authority who's supposed to have made this prediction, and I still don't see why the failure of that prediction would be strong evidence against the hypothesis that HIV-1 group M subtype C likely has a higher transmissivity than HIV-1 group M subtype B. Non-zero evidence? Yes. Decisive evidence? No.

Comment author: Azathoth123 26 August 2014 01:06:46AM 2 points [-]

I don't give that point any more weight than the last time you raised it (which I can't link because the relevant post got deleted). Now, as then, you haven't cited any specific person or authority who's supposed to have made this prediction, and I still don't see why the failure of that prediction would be strong evidence against the hypothesis that HIV-1 group M subtype C likely has a higher transmissivity than HIV-1 group M subtype B.

So why hasn't HIV-1 group M subtype C spread out of Southern Africa?

Comment author: satt 27 August 2014 10:37:07PM 3 points [-]

So why hasn't HIV-1 group M subtype C spread out of Southern Africa?

That question assumes a false premise. HIV-1 group M subtype C has spread out of Southern Africa.

Perhaps what you were trying to ask was why subtype C hasn't spread as aggressively as you personally expect beyond Southern Africa, though the information I gave two comments ago suffices to answer that question. Still, I will build on that information to spell this out.

The transmissibility of an HIV subtype is not the only factor determining how, and how far, that subtype spreads; behavioural differences between populations also matter. Southern African populations more often engage in non-circumcision and multiple concurrent partnerships than people elsewhere, and that combination of behaviours is the most likely reason why subtype C hasn't run riot among heterosexuals outside of Southern Africa (and Ethiopia & India).

If I leave things there, I suspect, I can look forward to a follow-up attempt at a dubious gotcha question along the lines of "So why bring up the transmissibility differences in the first place?". Because the fact remains that relative transmissibility is probably a factor in explaining why subtypes B & C have different spatial distributions. I had thought it clear that I was invoking relative transmissibility as merely a probable secondary factor, since I mentioned it parenthetically and wrote it "likely played a role", not that it was a sufficient, primary explanation in its own right.

Comment author: Azathoth123 29 August 2014 02:17:56AM 2 points [-]

Southern African populations more often engage in non-circumcision and multiple concurrent partnerships than people elsewhere, and that combination of behaviours is the most likely reason why subtype C hasn't run riot among heterosexuals outside of Southern Africa (and Ethiopia & India).

What about western groups that have many sexual partners, e.g., the swinger and polyamory communities?

Comment author: satt 30 August 2014 03:32:28PM 1 point [-]

What about western groups that have many sexual partners, e.g., the swinger and polyamory communities?

Your question blurs the distinction between promiscuity and multiple concurrent partnerships — I assume that was an accident.

Which precise question are you asking? Are you asking why Western groups with MCPs and low circumcision rates don't have (much) subtype C? If so, I'd like some specific evidence that they don't — it's a good idea to establish a phenomenon occurs before trying to explain it, and I'm having trouble finding systematic evidence on the HIV subtypes found among Western polyamorous people & swingers. If your question is about something subtly different (e.g. if you're asking about HIV in general among those groups, not subtype C in particular), please clarify.

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