Monday, July 18, 2011

The Sound of a One Legged Argument Kicking Itself

As I mentioned in yesterday's blog, a recent article finds evidence for the concurrency hypothesis 'compelling', despite liberal use of words that suggests a lot of doubt. The hypothesis is that lots of unsafe sex alone, involving numerous partners, low condom use, etc, does not account for high HIV prevalence; but if sexual relationships overlap with each other, HIV transmission will be very high.

A lot of work has been done to show that the concurrency hypothesis is entirely unsupported by evidence, particularly work by Eileen Stillwaggon and Larry Sawers. But in the article mentioned yesterday, Mah and Shelton dismiss anything challenging the hypothesis rather than addressing the failure of all the arguments that claim to support it.

Well, an article just published by Frank Tanser and colleagues finds that there is "no evidence to suggest that concurrent partnerships are an important driver of HIV incidence in [a] typical high-prevalence rural African population." But instead they argue that multiple partnerships are an important driver of incidence.

While Mah and Shelton denied that non-sexually transmitted HIV plays an important role in hyperendemic scenarios, without arguing the case, Tanser and colleagues don't even mention the possibility of non-sexual transmission. While obligingly neutralizing an argument that should never have been given much credence, and one that has been convincingly refuted by others, they seem to be taking a step backwards.

We have been hearing the oversexed African hypothesis for several decades now, it even predates the identification of HIV. So all Tanser has done is revived that tired old reflex as an explanation of massive rates of HIV transmission. But what is it about Africans that results in a virus that is difficult to transmit sexually spreading so fast in a population in which sexual behavior is little different from that found in many other low HIV prevalence populations?

Rates of new infections per year for both males and females in the study population are shockingly high But the researchers don't appear to have established how HIV was being transmitted. They have just assumed that transmission is all through heterosexual sex and then attempted to work out how risky heterosexual sex is among participants. But why is heterosexual sex so risky there? We are not told.

The authors find that "More than 24% of the adult population are infected with HIV and infection peaks at more than 50% in women aged 25–29 years and 44% in men aged 30–34 years." Given the fairly low probability of sexual transmission of HIV, 80 or 90% of women must be exposed to HIV if such high percentages end up infected.

The fact that male prevalence peaks in an older age group than female prevalence is sometimes explained by the 'fact' that older men have younger partners. But only some men have younger partners. Some have partners the same age as themselves. Like a lot of HIV related data, you could be forgiven for thinking that HIV in males is a different virus from HIV in females.

Despite flogging the dead horse of concurrency, which is worthwhile when you consider how much credence it still seems to have in the HIV industry, the authors remark that concurrency may have played a big part in earlier stages in high prevalence epidemics. But earlier treatment of the concurrency hypothesis suggest otherwise, so this concession doesn't exactly strengthen their argument for a return to the promiscuity theory of HIV.

And when it comes to their recommendations for HIV prevention strategy they really seem to weaken. They argue that 'messages' shouldn't be 'diluted'. Pumping out a fairly undiluted though highly stigmatizing message about HIV for many years has not resulted in UNAIDS having much success in reducing transmission, despite spending billions. In fact, the pharmaceutical lobby trying to increase drug use in the pretence that it will reduce transmission even refers to the institution's prevention work as a failure.

Telling people the truth about HIV transmission is not 'diluting' anything. If people are at risk they need to know about the risks and how to avoid them. UNAIDS have used the issue of 'dilution' as a reason for denying non-sexual risks, with the result that most people don't know that such risks exist, and therefore cannot avoid them. HIV prevention is not just an advertising campaign, even if it's never looked much different from one.


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