Background: Phylogenetic analyses of HIV gene sequences can be used to infer putative transmission clusters, with associated individual characteristics used to identify risk factors for HIV transmission. We hypothesized that HIV-infected adolescents would be linked to clusters of infected adults.
Methods: Data from time of first HIV genotyping for drug-resistance, including demographics (age, sex, race), HIV transmission risk (men who have sex with men (MSM), MSM & intravenous drug use (IDU), IDU, heterosexual), and homelessness were obtained from the University of Washington (UW) HIV Information System and retrospective chart review. HIV pol sequences were obtained from the UW Clinical Virology Laboratory. Phylogenetic clusters were defined as sequences with a shared ancestral node, support values >95% and pairwise genetic distances ≤0.015 nucleotide substitutions per site. The characteristics of all individuals found in clusters were compared to those of non-clustering individuals using multivariable logistic regression. This process was repeated for clusters with ≥1 adolescents (defined at age 13-24 year at first genotyping).
Results: There were 3116 total HIV-1 pol sequences from 1960 individuals, including 115 adolescents, genotyped between February 1, 2000 and March 1, 2013. Fifty-four phylogenetic clusters (containing 169 individuals) were identified. In unadjusted analyses, significant associations existed between cluster membership and adolescent age, MSM, and MSM&IDU. In adjusted analyses including transmission risk group, sex, homelessness, and age class at sequencing (adolescent or adult), adolescent age, MSM and MSM&IDU remained significantly associated with cluster membership.
Fifteen clusters were identified that included ≥1 adolescent; adolescents were 75% male, 57% MSM, 7% IDU, and 12% MSM&IDU. Considering those individuals in these clusters that were not adolescents (i.e. individuals that were adults), there was a non-significant positive association between MSM risk group (adults) and cluster membership.
Conclusions: This study suggests that MSM and MSM&IDU adolescents are at particularly high risk of HIV infection and may require specialized HIV prevention services.