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Editorial
. 2009 Oct;85(6):408-10.
doi: 10.1136/sti.2009.037499.

The role of heterosexual anal intercourse for HIV transmission in developing countries: are we ready to draw conclusions?

Marie-Claude Boily, Rebecca F Baggaley, Benoit Mâsse
Editorial

The role of heterosexual anal intercourse for HIV transmission in developing countries: are we ready to draw conclusions?

Marie-Claude Boily et al. Sex Transm Infect. 2009 Oct.
No abstract available

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Figures

Figure 1
Figure 1
A) Cumulative risk of HIV acquisition for females over three months (assuming 100% of sex acts with a HIV positive partner) as a function of the relative increase in per-act HIV transmission probability per receptive anal intercourse (AI) compared to receptive vaginal intercourse (VI). The figure shows that AI, practiced at a rate similar to what was reported in this study(1), can rapidly increase the cumulative risk of HIV infection within a relationship with a HIV positive partner. The cumulative risk is derived by CumRisk = 1 ((1 − pv)nact* fv · (1 − RRa · pv)nact* fa where pv= per-act male-to-female vaginal transmission probability; nact = total number of unprotected sex acts in three months; fv and fa (fv=1 − fa) are the fractions of sex acts which are vaginal and anal respectively and RRa is the increase in risk per-act for AI compared to VI. RRa = pa/pv where pa= per-act receptive AI transmission probability. We assumed nact=8.17 unprotected sex acts over three months of which 43% are AI (fv=56%, fa=43%) (as reported by Kalichman et al for women reporting AI (1)); the assumed male-to-female per-act HIV transmission probability for VI is set to the developed country estimate of pv=0.08%(12). B) Relationship between cumulative risk of HIV acquisition for females in the intervention arm during a hypothetical microbicide trial of different durations (x-scale) where 0%, 1%, 5%, 10% and 20% of sex acts are receptive anal intercourse (AI), when the microbicide has 80% efficacy when used vaginally and adherence is 100% for vaginal intercourse but 0% for AI. We assumed that 2.0 acts/week are not protected by condoms and that 25% of all acts are with HIV-infected partners. Male-to-female VI transmission probability is assumed to be 0.3%, as for developing countries and 1.7% for AI(12). The dark solid line represents the risk in absence of AI (0%) which when compared to the trial arm without microbicide (not shown) produces an effectiveness of 79% and 78% in a trial of 1 and 3 years respectively. The cumulative risk is calculated using a similar method to that used for Figure A, allowing for reduced per-act transmission probability according to efficacy of microbicide (further details in (13)).
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Comment on

References

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