HIV Sexual Networks: The Montreal Experience

While highly active antiretroviral therapy (HAART) has transformed HIV/AIDS to a chronic, treatable disease in Canada, HIV incidence continues to rise among male-sex-male (MSM) populations. Montreal, Canada, is a unique environment for a comprehensive surveillance study on HIV transmission dynamics. Phylogenetic strategies show that half of all new MSM infections in Montreal may arise through onward transmission by individuals who are in primary HIV infection (PHI) (< 6 months post-infection) and often unaware of their HIV status. Large cluster networks, wherein one infection leads to 5-31 onward transmissions, constitute the fastest-growing sub-epidemic, representing 25% and 39% of genotyped incident infections in 2005 and 2009, respectively. This has disturbing implications in light of the introduction of non-B subtype and drug-resistant sub-epidemics. Biological and behavioural correlates of cluster membership are being investigated to establish risk determinants implicated in the onward transmission of the MSM epidemic. Our findings underscore the opportunities and challenges in implementing new testing and tailored prevention paradigms for different MSM populations.