Background:  Our past findings, using population-based genotypic surveillance, estimated acute/recent infection to be a critical period for onward spread of the men-who-have-sex-with-men (MSM) epidemic in Quebec. Infections appear highly transmissible and individuals unaware of their status may engage in high-risk behaviors. This study combined molecular phylogenetic and epidemiological approaches to model MSM transmission dynamics and prevention interventions.

Methods:  HIV sequence data were obtained from primary HIV infections (PHI, <6 months post-infection) collected from the Quebec genotyping program (2002 to 2009, n = 1127). Phylogenetic analysis of male only, subtype B infections inferred MSM transmission dynamics (n = 922). Bayesian analysis using the BEAST package showed partial sampling is not detrimental to inference and time stability of infection dynamics. Behavioral determinants of clustering was assessed using risk profiles reported by MSM participants in the primary HIV-infection (PHI) cohort (n = 126). Changes in risk behaviors were determined at 5 time points (0, 6, 12, 18, and 24 months) following diagnosis.

Results:  Clustering of PHI represented 50% and 66% of transmissions in 2005 and 2009, respectively.  Phylogenetic analysis stratified MSM into non-clustered (n = 321); small clustered (2 to 4 PHI/cluster, 2.4 ± 0.8 PHI, n = 203) and large clustered (≥5 PHI/cluster, 9.9 ± 1.2 PHI/cluster, n = 398) transmission events. Large clusters rose from of 30% of transmissions in 2005 to 43% of PHI in 2009. Cohort participants reporting >10 partners, 3 months prior to diagnosis were more frequent in large clusters as compared to the other 2 groups (39% vs. 13%, odds ratio 4.67, P <0.001). Higher frequencies of insertive sex were reported by participants in the small cluster as compared to the other 2 groups (54% vs. 16%, odds ratio 9.3, p <0.01). Significant declines in anal and oral receptive risk behaviors, coupled with increased condom use were observed in all groups and sustained over >12 months. Little change in insertive sex was reported over time. In Montreal, 1/3 persons were unaware of their status at diagnosis and <30% had not had an HIV test one year prior to diagnosis.

Conclusions:  Molecular epidemiology findings have revitalized efforts to avert PHI-associated HIV transmissions. Rapid anonymous HIV testing with structured counseling administered by nurses and counselors, trained on MSM dynamics, at a new community site has been created to improve testing access with structured behavioral interventions.