A new Lancet Series published to coincide with the AIDS2012 meeting highlights a population where the HIV epidemic is growing in countries of all incomes: men who have sex with men (MSM). The first paper in the Series charts the epidemiology of HIV among MSM, and is by Professor Chris Beyrer, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA, and colleagues.
The authors conclude that differences between the HIV epidemic in MSM and other populations cannot be explained only by behavioural factors like condom use and multiple partners. The biology of HIV transmission in anal sex, MSM network features, and their related dynamics are key drivers, meaning that reducing infectiousness through initiatives like treatment as prevention and pre-exposure prophylaxis are likely to be key in curbing HIV in MSM.
Some countries reporting data have a HIV prevalence among MSM of 15% or higher: including the USA, Spain, Chile, Thailand, Malaysia, South Africa, and a cluster of other African and Caribbean nations. Italy, Brazil, India, and Canada are among nations with a prevalence of 11-15%. Across most of Western and Northern Europe, the range is 1-6%, including the UK. The region with the highest prevalence of HIV in MSM is the Caribbean (25%) followed by Africa (18%) and North America (15%). Western and Central Europe has a prevalence of 6%.
In many high-income settings—including Australia, France, the UK, and the USA—overall HIV epidemic trends are in decline except in MSM, where they have been expanding even in this modern era of highly active antiretroviral therapy (HAART). These increasing HIV infection rates have been have been described as re-emergent epidemics in MSM. In the USA, HIV infections in MSM are estimated to be increasing at roughly 8% per year since 2001. And in much of Africa, Asia, and Latin America, the highest rates of HIV infection in any risk group are in these men.
Well-documented risk factors for HIV infection among MSM include unprotected receptive anal intercourse, high frequency of male partners, high number of lifetime male partners, injection drug use, high viral load in the index partner, African-American ethnic origin (in the USA), and non-injection drug use, including use of amphetamine-like substances (ATS). But these risks alone are insufficient to explain the dramatic differences between HIV epidemics among MSM and other populations.