Modelling the transmission of HIV/STIs among men who have sex with men (MSM) in Southern India and Peru, and exploring the potential impact of different intervention strategies

Modelling the transmission of HIV/STIs among men who have sex with men (MSM) in Southern India and Peru, and exploring the potential impact of different intervention strategies
Funders: Support for this research has been provided by the American Foundation for AIDS Research (amfAR) and the Wellcome Trust, the Microbicides Development Programme (MDP), funded by the UK Department for International Development (DFID) and the UK Medical Research Council (MRC), and some researchers involved are also members of DFID-funded RPC.

Collaborators: London School of Hygiene & Tropical Medicine, UK, Imperial College London, UK, Karnataka Health Promotion Trust, Bangalore, India, St John’s Research Institute, Bangalore, India, University of Manitoba, Winnipeg, Canada, IMPACTA, Lima, Peru, University of Washington, USA, HIV Prevention Trials Network (HPTN 039), sponsored by the National Institutes of Health, U.S. Department of Health and Human Services.

Data: The Bangalore data were collected as part of the monitoring and evaluation of Avahan, the India AIDS initiative, funded by the Bill & Melinda Gates Foundation, and the Lima data were from the sentinel surveillance and supplemented with data from HPTN 039.

Modelling the potential impact of a rectal microbicide used by MSM in Bangalore, India, and Lima, Peru

No prior research existed outlining the potential impact of rectal microbicides on the HIV epidemic in a low- or middle-income country setting. This project used detailed epidemiological and behavioural data from Bangalore and Lima—two settings in which the HIV epidemic remains concentrated in high-risk groups including MSM—to parameterise and fit a compartmental epidemiological model. The joint transmission dynamics of HIV, syphilis and genital herpes were simulated between three behavioural subgroups of MSM, defined by their typical role taken during anal sex—insertive, receptive or both. The potential evolution of the HIV epidemic was investigated with and without a five-year rectal microbicide intervention. Various scenarios of microbicide availability, consistency of use and per sex act efficacy against HIV were explored, as well as the potential effects of substituting microbicide use for condom use.

Despite large differences across settings, if condom use is maintained following microbicide introduction, the model projected that the percentage of infections averted would be similar in both Bangalore and Lima.

For example, the preliminary model predicts that a 60% HIV-efficacious microbicide accessed by 30% of MSM and used in half of non-condom-protected sex acts could avert about 12% of HIV infections among MSM in both settings over 5 years, if condom use remains at pre-microbicide levels. However, if 20% fewer sex acts are condom-protected after microbicide introduction (and other factors remain the same), then impact lessens, and HIV infections are predicted to increase among MSM in Lima (by about 10%).

The potential indirect impact of rectal microbicide use among these men, in terms of lowering HIV/STI prevalence among MSM to reduce transmission to their wives/cohabiting female partners, typically offers only marginal benefits to these women.

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 HIV/STI risk. The findings highlight the importance of pursuing further research and investment for developing rectal microbicides. Vaginal microbicides that could be used by the female partners of MSM would likely also be an important breakthrough, since condom use is reported to be low in these partnerships but underlying risk is high.

Further details were presented at the Microbicides 2010 conference in May 2010 and as a poster at the AIDS 2010 conference.

Using modelling to explore the transmission dynamics of HIV among MSM in a Southern Indian setting

Emerging research from Southern India highlights that there is considerable ‘behavioural heterogeneity’ among men who have sex with men (MSM), defined as differences in anal sex roles (insertive/receptive) and involvement in commercial sex and sex with women. Mathematical modelling, using new detailed behavioural and biological data from Bangalore, will explore:

1) To what extent does behavioural heterogeneity influence the HIV epidemic among MSM and more widespread transmission?

2) How sensitive are transmission patterns and projected intervention impacts to the level of heterogeneity modelled and key assumptions?

3) What are the implications for MSM interventions, and future research and prevention priorities?