Modelling the potential impact on HIV transmission of rectal microbicide use by men who have sex with men, and the effects of condom substitution

Published: July 22, 2010

Modelling the potential impact on HIV transmission of rectal microbicide use by men who have sex with men, and the effects of condom substitution

Background: In India and Peru the HIV epidemic remains concentrated in high-risk groups including men who have sex with men (MSM). Given the challenges of condom use, interest has grown on the potential role of a rectal microbicide for MSM. There are no previous estimates of the likely public health impact of a rectal microbicide in any low- or middle-income country.
Methods: Detailed epidemiological and behavioural data from Bangalore and Lima were used to parameterise and fit a deterministic compartmental model. The joint transmission dynamics of HIV, syphilis and herpes were simulated between three behavioural subgroups of MSM. Potential evolution of the HIV epidemic was investigated with and without a 5-year microbicide intervention. It was assumed that 30% of the total MSM population would be reached by the intervention and various scenarios of efficacy and consistency of use were explored.
Results:

Average consistency of microbicide use in non-condom protected MSM anal sex acts amongst reached MSM Per sex act efficacy of microbicide for reducing HIV transmission to receptive partner Percentage of HIV infections averted among MSM in BANGALORE Percentage of HIV infections averted among MSM in LIMA Percentage of HIV infections averted among MSM in BANGALORE Percentage of HIV infections averted among MSM in LIMA
    Condom used in same percentage of MSM anal sex acts after microbicide introduction as before (60%) Condom used in same percentage of MSM anal sex acts after microbicide introduction as before (70%) Condom used in 20% fewer MSM anal sex acts after microbicide introduction (48%) Condom used in 20% fewer MSM anal sex acts after microbicide introduction (56%)
50% 35% 7.1% 7.5% -3.8% -18.5%
50% 85% 17.0% 17.9% 9.5% -1.6%
100% 35% 14.0% 14.8% 5.6% -6.6%
100% 85% 32.7% 34.2% 30.7% 25.1%

[Table: Preliminary model projections]

The table illustrates that an 85% efficacious microbicide used in half of non-condom-protected sex acts could avert over 17% of HIV infections among MSM in both settings if condom use remains at pre-microbicide levels. However, if 20% fewer sex acts are condom-protected after microbicide introduction, then impact lessens, and HIV infections are predicted to increase among MSM in Lima.
Conclusions: This study highlights the importance of pursuing further research and investment for developing rectal microbicides. The public health benefit from an effective rectal microbicide could be considerable if used consistently, but condom use must be maintained in order to avoid potentially increasing risk.

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