Open Thread, September, 2010-- part 2

NancyLebovitz

This thread is for the discussion of Less Wrong topics that have not appeared in recent posts. If a discussion gets unwieldy, celebrate by turning it into a top-level post.

However, the typical estimates of transmission rate are extremely low: 0.05% / 0.1% per insertive/receptive P/V sex act 0.065% / 0.5% per insertive/receptive P/A sex act

These transmission rates are so astronomically low that for it to spread from one infected person to an uninfected partner would take years and years of unprotected sex.

At an (unrealistically?) independent 0.5% chance per act, a 50% chance of transmission would require 139 sex acts — hardly "years and years".

(ETA: yes, unrealistically, according to this abstract found by Perplexed: "However, in comparison with nonparametric estimates, the model assuming constant infectivity appears to seriously underestimate the risk after very few contacts and to seriously overestimate the risk associated with a large number of contacts. Our results suggest that the association between the number of unprotected sexual contacts and the probability of infection is weak and highly inconsistent with constant per-contact infectivity.")

So in my mind this makes it technically impossible for HIV to be an STD.

At best, this can show that pandemic AIDS can't primarily result from sexual transmission of HIV, which is evidence that AIDS has causes other than HIV, but also that pandemic AIDS spreads through other means (as suggested here, e.g.).

As gonorrhea (and I presume other STDs) are hundreds of times more transmissable than HIV, their low rates in the population place bounds on HIV's sexual transmission.

If you're thinking of rates in the modern developed world, STDs are unsurprisingly more common when and where treatment is less available:

...in New York City, serologic testing in 1901 indicated that 5%-19% of all men had syphilitic infections. (source)

Studies of pregnant women in Africa have found rates for gonorrhea ranging from 0.02% in Gabon to 3.1% in Central African Republic and 7.8% in South Africa.... [syphilis] rates of 17.4% in Cameroon, 8.4% in South Africa, 6.7% in Central African Republic and 2.5% in Burkina Faso.... (source)

At an (unrealistically?) independent 0.5% chance per act, a 50% chance of transmission would require 139 sex acts — hardly "years and years".

I don't see why epidemiology should care about the 50% threshold. The relevant number is the expected number of transmissions per year. Thus independence is irrelevant.[1] At 200 anal tops per year per infected person, incidence should double yearly. And every top requires a bottom, so that's 400 anal sex acts per year for just doubling. It seemed to spread more quickly than that, but maybe 800 and 4x per... (read more)

3jacob_cannell16y

That is for the highest transmission activity - receptive A, so be careful not to cherry pick. Yes - 139 unprotected sex acts. It would take 1390 unprotected insertive A sex acts to reach a 50% chance of transmission. So with some assumptions, mainly - gay bathouses and no condom use - yes the virus could spread horizontally, in theory. Although that population would necessarily first acquire every other STD known to man, more or less. But in the general heterosexual population, not a chance. If you compare to the odds of pregnancy from unprotected sex, the insane requisite amounts of unprotected sex with strangers would result in a massive baby epidemic and far more vertical transmissions long before it could ever spread horizontally in the hetero population. I don't know why you mention "modern developed-world rates" and then have a link to 1901 NY and Africa . . . [...] You don't need the "at best" qualifier, but yes I agree that is what this shows. Showing that however opens a crack in the entire facade. Perhaps not a critical failure, but a significant doubt nonetheless. If the orthodox position had updated on the evidence, and instead changed their claim to "HIV is a borderline infectious disease that spreads primarily through the prenatal and blood-borne routes", then I would give them more creedence. Of course, for political reasons alone they could never admit that.