When you plot a graph with UNAIDS' prevalence figures for HIV country epidemics using the figures available for 1990-2007, for most sub-Saharan African countries there is a pronounced hump where prevalence peaks, followed by a downward trend, presumably where death rates began to rise (it was far too early for declines to be much related to prevention programs). As you can see from the graph below, prevalence reached almost 30% in Zimbabwe; in Tanzania, figures never rose higher than 8%.
According to UNAIDS and the received view of HIV epidemics, the virus was spread rapidly as a result of high and increasing levels of unprotected heterosexual sex. Explanations of why levels of unprotected sex should have increased suddenly, and then declined, are not so clear. There are vague mentions of urbanization, changes in social norms, migration and all sorts of other things. However, there is little indication about why these might have changed so profoundly when they did, and none at all about why they changed back again to the way they were before (which they must have done if the received view is true).
Given all this rampant sex, you'd expect at least a slight uptick in birth rates, right? Contraceptive use was also increasing in the 70s, 80s and 90s, but not so fast; it's still not that high in many countries. Well, fertility rates have actually been declining for decades in places like Tanzania and Zimbabwe. The graphs linked to, far from showing any hump, clearly show a decline, from an average of just under 7 births per woman in 1960 to 5.5 in 2010 in Tanzania and from just over 7 in 1960 to 3.3 in 2010 in Zimbabwe.
When HIV prevalence was peaking in the 1990s, fertility continued a steep decline that began several decades before. But given the continued high rates of unprotected heterosexual sex, demonstrated by continued high birth rates in Tanzania, you might be led to expect high HIV prevalence there. Instead, the figures are substantially lower than they are in Zimbabwe, which has one of the worst HIV epidemics in the world.
Of course, these figures are rough. HIV epidemics are characterized by considerable heterogeneity; figures vary enormously between age groups, genders, tribes, religious groups, etc, and also in different areas. But there are still anomalies with the 'behavioral paradigm', the view that HIV is almost always transmitted through heterosexual sex (in African countries; the caveat needs to be in brackets, because it is generally unspoken, but HIV is most definitely not almost always transmitted through heterosexual sex in non-African countries).
For example, fertility tends to be higher in rural areas, whereas HIV prevalence tends to be higher in urban areas. HIV prevalence is generally higher among females in high prevalence African countries, but unsafe sexual behavior rates are generally higher among males. Women may face higher risks than men, but if they are almost always infected by men, rates among men shouldn't be too much lower than among women.
There was an interesting paper published a couple of years ago, entitled "Sexual behaviour does not reflect HIV-1 prevalence differences: a comparison study of Zimbabwe and Tanzania", by Munyaradzi P Mapingure, et al. And this paper found that, despite HIV rates being far higher in Zimbabwe, rates of 'unsafe' sexual behavior were far higher in Tanzania. In fact, rates of almost all sexual risk factors for HIV were higher in Tanzania than in Zimbabwe. The authors conclude that non-sexual HIV transmission may play an important role in variations in HIV prevalence.
It's interesting that the authors should make such a suggestion because there's a Wikileaks cable about HIV transmission through reused syringes in health facilities in Nigeria, written by President Obasanjo to President Bush. Obasanjo was proposing the use of autodisable syringes, which break after being used once, because the WHO estimated that nearly half of all syringes are reused in Africa and that 10% of new HIV infections are from contaminated blood, including unsafe injections.
Nigeria has the third highest number of people living with HIV in the world, behind South Africa and India. 10% represents a lot of infections through unsafe healthcare. According to UNAIDS estimates, unsafe healthcare only accounts for around 2.5% of HIV transmission. But, given Mapingure's paper, along with the distinct lack of increased birth rates at a time when massive increases in unsafe sex were said to have been causing so many appalling HIV epidemics, which are still out of control in most high prevalence countries, perhaps it's time to take another look at the relative contribution of sexual and non-sexual HIV transmission?
[For more about non-sexual HIV transmission and mass male circumcision, see the Don't Get Stuck With HIV site.]