Transmission clustering drives the onward spread of the HIV epidemic among men who have sex with men in Quebec.

Phylodynamic analysis and epidemiologic data identified 3 patterns of spread of primary human immunodeficiency virus type 1 infection (PHI) among men who have sex with men (2001-2009): 420 unique PHIs, 102 small clusters (2-4 PHIs per cluster, n = 280), and 46 large clusters (5-31 PHIs per cluster, n = 450). Large clusters disproportionately increased from 25.2% of PHIs in 2005 to 39.1% in 2009 (χ(2) = 33.9, P < .001). Scalar expansion of large clusters over 11 months (interquartile range, 3.5-25.5 months) correlated with cluster membership size (r(2) = 0.174, F = 4.424, P = .047). PHI cohort data revealed variations in social networks and risk behaviors among the 3 groups, suggesting the need for tailored prevention measures.

Transmission networks of drug resistance acquired in primary/early stage HIV infection.

OBJECTIVES: Population-based sequencing of primary/recent HIV infections (PHIs) can provide a framework for understanding transmission dynamics of local epidemics. In Quebec, half of PHIs represent clustered transmission events. This study ascertained the cumulative implications of clustering on onward transmission of drug resistance. METHODS: HIV-1 pol sequence datasets were available for all genotyped PHI (<6 months postseroconversion; n = 848 subtype B infections, 1997-2007). Phylogenetic analysis established clustered transmission events, based on maximum likelihood topologies having high bootstrap values (>98%) and short genetic distances. The distributions of resistance to nucleoside and nonnucleoside reverse transcriptase inhibitors and protease inhibitors in unique and clustered transmissions were ascertained. RESULTS: Episodic clustering was observed in half of recent/early stage infections from 1997-2008. Overall, 29 and 28% of new infections segregated into small (<5 PHI/cluster, n = 242/848) and large transmission chains (> or =5 PHI/cluster, n = 239/848), averaging 2.8 +/- 0.1 and 10.3 +/- 1.0 PHI/cluster, respectively. The transmission of nucleoside analogue mutations and 215 resistant variants (T215C/D/I/F/N/S/Y) declined with clustering (7.9 vs. 3.4 vs. 1.2 and 5.8 vs. 1.7 vs. 1.1% for unique, small, and large clustered transmissions, respectively). In contrast, clustering was associated with the increased transmission of viruses harbouring resistance to nonnucleoside reverse transcriptase inhibitors (6.6 vs. 6.0 vs. 15.5%, respectively). CONCLUSION: Clustering in early/PHI stage infection differentially affects transmission of drug resistance to different drug classes. Public health, prevention and diagnostic strategies, targeting PHI, afford a unique opportunity to curb the spread of transmitted drug resistance.