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Misinformation from UNAIDS’ flawed Modes of Transmission model

To defeat HIV/AIDS in Africa, UNAIDS recommends: “Know your epidemic.” The best way to do so is to investigate to trace the source of infections – especially in children with HIV-negative mothers, virgins, and married people with HIV-negative spouses and no outside partners.

But that’s not what UNAIDS urges African governments to do. Instead, UNAIDS urges governments to use its Modes of Transmission (MOT) model to estimate numbers of infections from various risks.

But the MOT model contains a glaring error. Because of this error, whoever uses the model ends up estimating far too many infections coming from spouse-to-spouse transmission.

In Uganda, for example, the MOT model estimates that 60,948 married adults got HIV from their spouses during 2008. This is two-thirds of the model’s estimated total new infections from all risks in Uganda in 2008.

The MOT model got this number by supposing that 5.9% of married adults (421,000 adults) were HIV-negative with HIV-positive spouses, and that 14.5% of these spouses at risk got HIV from husbands or wives in 2008 (60,948 = 14.5% x 421,000).

But the number of spouses at risk is far, far less. Uganda’s 2004/5 HIV/AIDS Sero-behavioral Survey reports that 6.2% of husbands and 5.2% of wives were HIV-positive.  But – and this is the important fact the MOT model ignored – most HIV-positive husbands and wives were married to each other. Only 2.8% of wives and 1.8% of husbands were HIV-negative with HIV-positive spouses.

Overall only about 2.3% of married adults (averaging 2.8% of wives and 1.8% of husbands) were HIV-negative with HIV-positive spouses – only 222,000 vs. the 421,000 estimated in the MOT model. If 14.5% of these 222,000 adults got HIV from their spouses in a year, that would account for 32,100 new infections (14.5% x 222,000), far less than the 60,948 estimated in the MOT model.

Why is this important? Because if fewer infections are coming from spouses, how did so many Ugandans get HIV in 2008? In other words, the MOT not only over-estimates HIV from spouses, but also underestimates infections from other risks.

What risks are underestimated? Hold on now! Don’t run away with sexual fantasies about young people and some married adults having too much fun with non-spousal partners. Indulging in racist and stigmatizing sexual fantasies is something too many official AIDS experts like to do. But the evidence does not support such fantasies. The best information on sexual behavior does not come close to explaining Uganda’s epidemic.

Setting aside sexual fantasies, the underestimated risks are more likely to be those that UNAIDS’ staff and other health professionals want to ignore – skin-piercing procedures with unsterile instruments, such as injections, dental care, manicures, etc. This is true not only in Uganda but also in more than 15 other African countries that have used the MOT model to get ridiculous figures on numbers of HIV infections from spouses.

Remember how we began: The best way to “know your epidemic” is to trace infections. Let’s challenge HIV/AIDS researchers — finally — to do their job. Although it’s decades too late, tracing is still needed to find all the important risks and to stop Africa’s generalized HIV/AIDS epidemics.

[Note: This blog summarizes evidence and arguments in: Gisselquist D. UNAIDS’ Modes of Transmission model misinforms HIV prevention efforts in Africa’s generalized epidemics, available at:]

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