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Structural factors present major challenges for reducing HIV burden in MSM
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Men who have sex with men continue to be disproportionally affected by HIV, even in the face of declining rates among the general population, according to findings presented here by Stefan D. Baral, MD.
Baral, of the Center for Public Health and Human Rights at Johns Hopkins Bloomberg School of Public Health, presented results of a study in The Lancet that was a comprehensive review of available data for HIV prevalence, incidence, risk factors and the molecular epidemiology of HIV in MSM from 2007 to 2011. The researchers then modeled the dynamics of HIV transmission with an agent-based simulation.
Results indicated that a key driver of this epidemic was the high probability of transmission per act via receptive anal intercourse. “Baggaley and colleagues observed a 1.4% transmission rate per act, which is 18-fold higher than the rate with vaginal sex,” Baral said.
With this risk at hand, the virus may be transmitted quickly through large networks of MSM. “Men have sexual role versatility, which increases the efficiency of transmission,” Baral said. “MSM often play both the receptive and insertive roles, which increases both risk and the speed of transmission.”
Substantial clustering of HIV infections in MSM networks also was observed in molecular epidemiological data from the study. MSM were more likely to have dual-variant and multiple-variant HIV infections than heterosexuals in the same populations.
The researchers recommend prevention strategies aimed at lowering biological transmission and acquisition risks, including condom-based programs and approaches based on ART. However, they said structural factors prevent MSM from seeking this information in many parts of the world.
The researchers examined individual level, network level and structural risks. They found that individual behaviors were insufficient in explaining the massive changes among MSM. “When we started looking at the network level, we started to see the picture,” Baral said. “But then we began looking at emerging data indicating greater structural level risks. We saw incarceration and stigma, limitations of preventive services.”
There is a narrow range of HIV prevalence across most continents, according to Baral. “We saw a lot of consistency among populations and continents, with prevalence rates ranging from 7% to 14%,” he said. “But on all continents, even in sub-Saharan Africa, we see higher concentrations among MSM.”
The rates are increasing among MSM in the context of declining incidence rates in the general population, according to Baral. “We wanted to find out what were the drivers of this phenomenon,” he said. “We wanted to know why this is happening.”
References:
Baral S. #TUSY0701. Presented at: XIX International AIDS Conference; July 22-27, 2012; Washington, D.C.
Beyrer C. Lancet. 2012;doi:10.1016/S0140-6736(12)60821-6
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