Who mixes with whom among men who have sex with men? Implications for modelling the HIV epidemic in southern India

Abstract

In India, the identity of men who have sex with men (MSM) is closely related to the role taken in anal sex (insertive, receptive or both), but little is known about sexual mixing between identity groups. Both role segregation (taking only the insertive or receptive role) and the extent of assortative (within-group) mixing are known to affect HIV epidemic size in other settings and populations. This study explores how different possible mixing scenarios, consistent with behavioural data collected in Bangalore, south India, affect both the HIV epidemic, and the impact of a targeted intervention. Deterministic models describing HIV transmission between three MSM identity groups (mostly insertive Panthis/Bisexuals, mostly receptive Kothis/Hijras and versatile Double Deckers), were parameterised with behavioural data from Bangalore. We extended previous models of MSM role segregation to allow each of the identity groups to have both insertive and receptive acts, in differing ratios, in line with field data. The models were used to explore four different mixing scenarios ranging from assortative (maximising within-group mixing) to disassortative (minimising within-group mixing). A simple model was used to obtain insights into the relationship between the degree of within-group mixing, R0 and equilibrium HIV prevalence under different mixing scenarios. A more complex, extended version of the model was used to compare the predicted HIV prevalence trends and impact of an HIV intervention when fitted to data from Bangalore. With the simple model, mixing scenarios with increased amounts of assortative (within-group) mixing tended to give rise to a higher R0 and increased the likelihood that an epidemic would occur. When the complex model was fit to HIV prevalence data, large differences in the level of assortative mixing were seen between the fits identified using different mixing scenarios, but little difference was projected in future HIV prevalence trends. An oral pre-exposure prophylaxis (PrEP) intervention was modelled, targeted at the different identity groups. For intervention strategies targeting the receptive or receptive and versatile MSM together, the overall impact was very similar for different mixing patterns. However, for PrEP scenarios targeting insertive or versatile MSM alone, the overall impact varied considerably for different mixing scenarios; more impact was achieved with greater levels of disassortative mixing.

Optimal Allocation of Resources in Female Sex Worker Targeted HIV Prevention Interventions: Model Insights from Avahan in South India

“…Sensitivity analyses suggest the model’s simplicity did not adversely affect the model projections. Incorporating other behavioural heterogeneities is also unlikely to have affected the model findings [38] . Future analyses considering multiple interventions, HRGs and settings will use more complex models.…”

Using data from ‘visible’ populations to estimate the size and importance of ‘hidden’ populations in an epidemic: A modelling technique

“…The analysis is also somewhat limited by the lack of data about sexual mixing patterns, although previous modelling has shown that, for this setting, HIV prevalence projections are largely unaffected by the underlying mixing assumptions ( Mitchell, Foss, Prudden, et al., 2014 ). Insufficient data on other factors or inconsistent data due to different data collection methods ( Phillips et al., 2013 ) also presented a challenge, leading us to make necessary simplifying assumptions in the model to match data availability ( Garnett & Anderson, 1996 ) or having to obtain some model parameter estimates from nearby districts or state-level data.…”

“…As in our prior modelling analysis ( Mitchell, Foss, Prudden, et al., 2014 ), the size of the insertive MSM subgroup was set to balance the total number of insertive and receptive sex acts in the whole MSM/TGW population. The number of receptive sex acts reported by each subgroup were distributed among the three subgroups (as their partners) in proportion to the number of insertive acts reported by each (partner) subgroup.…”

HIV transmission and pre-exposure prophylaxis in a high risk MSM population: A simulation study of location-based selection of sexual partners

“…Characteristics of sexual networks, including density, homophily (by ethnicity, sexual behavior), concurrency and temporal structure impact the spread of infectious diseases [ 24 , 28 , 41 – 48 ]. Recently, assortativity by race or identity group has been explored in MSM as an explanation to differences in HIV spread in selected subpopulation [ 48 , 49 ]. Yet, substantial heterogeneity remains in HIV spread, calling for more research and data on the association of personal and network related risk factor of being infected by HIV.…”

“…Other individual characteristics (ethnicity, drug use, type of anal intercourse) [ 60 ] have been studied to help target those at risk of being infected and who would benefit the most from PrEP. Yet, these models did not investigate the role of the sexual network structure, which is indeed a more recent endeavor in models [ 26 , 43 , 49 ].…”