Characterizing clusters of HIV infection among men who have sex with men (MSM) in Montreal, Canada: source of clues for interrupting transmission dynamics?
J. Cox1,2, R. Allard2, S. Law1, C. Tremblay2, R. Pilon3, C. Archibald4, G. Lambert2, P. Leclerc2, M. Alary5, R. Remis6, P. Sandstrom3
1McGill University, Epidemiology, Biostatistics & Occupational Health, Montreal, Canada, 2Direction de la Santé Publique de Montréal, Secteur Vigie et Protection, Montreal, Canada, 3Public Health Agency of Canada, National HIV & Retrovirology Laboratories, Ottawa, Canada, 4Public Health Agency of Canada, Surveillance and Risk Assessment Division, Ottawa, Canada, 5Laval University, Département de Médecine Sociale et Préventive, Quebec, Canada, 6University of Toronto, Dalla Lana School of Public Health, Toronto, Canada
Background: Studying HIV transmission patterns through phylogenetic approaches can lead to a better understanding of infection dynamics in at-risk populations such as MSM. This study sought to determine the extent and correlates of HIV clustering among acute and chronically infected MSM in Montreal.
Methods: HIV protease and reverse transcriptase (RT) genes from specimens collected from Montreal MSM who participated in 2 studies: the Omega Cohort study (1996-2003), 29 acute (based on seroconversion/new positive HIV test), 28 chronic; and the Argus study (2005), 10 recent (using STARHS), 97 chronic. Self-administered questionnaires provided information on socio-demographic, attitudinal and behavioural factors. Multivariable logistic regression analyses [adjusted Odds ratio & 95% confidence intervals (aOR, CI)] estimated the associations between these factors and cluster membership.
Results: A neighbour-joining analysis identified 17 clusters (28% of cases). 31% of acute infections (2 with other recent) and 26% of chronic infections were clustered. Cluster size ranged from 2 to 5 members. In the final model (n=118) independent correlates of clustering were younger age in years (1.08 per year, 1.02-1.15) and ethnicity other than English or French Canadian (3.98, 1.37-11.58). Being in a couple with an HIV-positive man (one type of regular partner) compared to being in a couple with an HIV-negative man was marginally associated with cluster membership. Having at least one casual (one-night) sexual partner in the past 6 months was negatively associated with being in a cluster (0.06, 0.01-0.27).
Conclusions: Despite a small sampling fraction and a case distribution over many years, this study documented both HIV clusters and related traits. Factors such as ethno-cultural identity, age and recent behaviours (having a casual sexual partner) were found to characterize clusters and these factors may be related to ongoing HIV transmission among Montreal MSM. With larger and more representative samples, molecular phylogenetic analyses could prove useful in guiding prevention interventions.
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