Abstract Body

Background: The study of HIV transmission networks provides insight into the spread of HIV, and thus into opportunities for intervention. By identifying genetically similar HIV variants in large datasets, we can construct such transmission networks. Two persons infected with highly similar HIV variants are likely to have a direct or indirect epidemiologic connection and represent potential transmission partners. Transmission dynamics between people who are similar or different with respect to race/ethnicity, risk characteristics, and geography are unclear. To identify demographic and risk characteristics of potential transmission partners, we constructed a U.S. HIV transmission network. Methodology: We analyzed 41,294 HIV-1 pol sequences collected through the U.S. National HIV Surveillance System (NHSS) during 2001-2012. We aligned sequences (one/person aged ≥13 years) to a reference sequence (HXB2) and performed pairwise comparisons among all sequences. Possible linkages were defined by Tamura-Nei 93 genetic distance ≤1.5%. We constructed a transmission network and analyzed data on risk group (MSM, IDU, MSM/IDU, heterosexual), race/ethnicity, and state of residency at diagnosis for pairs of potential transmission partners. Results: The network contained 12,910 nodes (31% of all sequences) and 29,493 connections. MSM comprised 61% of persons with sequences but 76% of the network. In the vast majority of transmission pairs containing at least one MSM, the second person was also MSM (MSM: 82%, MSM/IDU: 7%) (Table). Heterosexual women were more commonly connected to MSM (44%) than to heterosexual males (18%) or IDUs (13%). MSM/IDU were far more commonly connected to MSM (88%) than to IDUs (2%). Transmission pairs containing blacks/African Americans were more racially homogeneous (63%) than pairs containing whites (47%) or Hispanics (27%). Of pairs, 82% consisted of two persons living in the same state at diagnosis; this percentage was higher for pairs with female IDUs (90%) and heterosexual women (91%). Conclusions: This analysis is the first use of NHSS data to infer an HIV transmission network. Geographic and racial/ethnic mixing in HIV transmission were present, although the extent varied by population. The majority of potential transmission partners connected to MSM were also MSM, but other risk groups were also commonly connected to MSM. Interventions that reduce transmissions by MSM are likely to reduce HIV acquisition among other risk groups as well.