The XVII International AIDS Conference (AIDS 2008)

Forced Sex Poses Five Times the HIV Risk Compared to Consensual Sex

An Interview With Anna Foss

August 5, 2008

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Can you tell me your name and where you're from, and a little bit about your poster?

I'm Anna Foss, from London School of Hygiene & Tropical Medicine, in the U.K. My poster is on "HIV/AIDS and Rape, and Modeling Predictions of the Increase in Individual Risk of Contracting HIV from Forced Sex."1 What we did here was a big literature review, looking at the different factors that might be involved -- from violence or forced sex -- in terms of increasing a woman's risk of acquiring HIV. In particular, looking at genital injury. We discovered that there's nothing in the literature that clarifies how genital injury might translate, to the per-sex act probability of HIV transmission.

Anna Foss
Anna Foss
Then we had to develop some scenarios or key assumptions of what we would include in the model. We were trying to be conservative in what we did and look at the fact that there's evidence that STIs [sexually transmitted infections] increase the risk of acquiring HIV, by about threefold. We thought: What if it's similar for multiple sites of trauma from forced sex? What if it's about half that, if there's a single site of trauma?

Then we said: What if the perpetrators -- because we've seen a lot of evidence in the other talks, by Charlotte Watts and others at the conference2 -- that perpetrators of sexual violence are more likely to have multiple partners, etc., so thus are more likely to have HIV and STIs than non-perpetrators. So we assumed that conservatively, maybe it's twice as likely that these perpetrators are infected.

When we did a comparison using this risk equation, we asked: What if we compare conflict scenario versus a comparison to a more consensual scenario? The conflict scenarios are based around things like forced sex and females selling sex to male members of a peacekeeping force, females being raped by men in a refugee camp; but also considering things like population movement. So you might have people moving from a higher exposed area to a lower exposed area, or the opposite of that.

You can see, actually, that with the risk ratios generated, some of them you can get as high as about four or five times risk because of the conflict, compared to if there had been no conflict. But you can sometimes get a reduction, because you have an influx of lower risk coming in.

So you found a risk ratio, in some cases, as high as 5.3. What's the typical general risk ratio for HIV acquisition for a sex act? How is this different from a typical act of unprotected sex?

The comparison is exactly what we've done here. We're comparing say, an adult female who is raped by three men in a refugee camp, and also has this low-risk male partner who is just her normal partner and she has three consensual sex acts with her low-risk male partner. But the additional risk in the conflict scenario is that she's also raped by three men at the refugee camp.

So what we're saying is that in this conflict scenario, because of the rape, she's five times more likely to contract HIV than if she's only had these consensual sex acts with her usual partner.

I think the key, if I could just sort of say the key kind of conclusions for me, really, is that we're looking at the individual's risk. I think other researchers are looking at population level, perhaps a prevalence, which isn't a very sensitive indicator, really. So here we're looking at an individual level.

The same with STI treatment, where sometimes at a population level, it's hard to see an effect. But individually STI treatment is helping to control HIV transmission. The scenarios, actually, because of the maths, a lot of factors cancel out -- a lot of the uncertainties cancel out -- and all you need to know, actually, is how much more likely is a perpetrator to have HIV or STI than a non-perpetrator, or how many more sex acts versus partners. It's lots of mathematical tradeoffs that cancel out the uncertainties, which is quite helpful really in trying to parameterize the model.

The key thing is really that rape and coercion should be considered in HIV programming, and we're trying to do this kind of quite simple scenario-based work just to highlight that and bring that to the forefront of the agenda a bit more.

It's been nice to see some of the panels, panel discussions and other presentations here, trying to raise this issue more and look more at structural interventions, beyond the biomedical, and looking more at the whole, the broader context, in which, are women able to say no to sex? And what effect does that have on the ABC [Abstinence, Be Faithful, Use Condoms], exactly, than the biomedical interventions?

Thank you very much.

This transcript has been lightly edited for clarity.


  1. Foss A, Von Simson R, Zimmerman C, Hossain M, Watts C. HIV/AIDS and rape: modelling predictions of the increase in individual risk of contracting HIV from forced sex in South Africa. In: Program and abstracts of the XVII International AIDS Conference; August 3-8, 2008; Mexico City, Mexico. Abstract TUPE0650.
  2. Ghanotakis E, Mayhew S, Watts C. Tackling HIV and gender-based violence in South Africa: organisational responses to PEPFAR. In: Program and abstracts of the XVII International AIDS Conference; August 3-8, 2008; Mexico City, Mexico. Abstract THAE0404.
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