HIV-1 Infection and Transmission Networks of Younger People in Chicago, Illinois, 2005-2011

Abstract

Objective: Analysis of HIV nucleotide sequences can be used to identify people with highly similar HIV strains and understand transmission patterns. The objective of this study was to identify groups of people highly connected by HIV transmission and the extent to which transmission occurred within and between geographic areas in Chicago, Illinois.

Methods: We analyzed genetic sequences in the HIV-1 pol region in samples collected from people participating in the VARHS program in Chicago during 2005-2011. We determined pairwise genetic distance, inferred potential transmission events between HIV-infected people whose sequences were ≤1.5% genetically distant, and identified clusters of connected people. We used multivariable analysis to determine demographic characteristics and risk attributes associated with degree of connectivity.

Results: Of 1154 sequences, 177 (15.3%) were tied to at least 1 other sequence. We determined that younger people, men, non-Hispanic black people, and men who have sex with men were more highly connected than other HIV-infected people. We also identified a high degree of geographic heterogeneity-48 of 67 clusters (71.6%) contained people from >1 Chicago region (north, south, or west sides).

Conclusion: Our results indicate a need to address HIV transmission through the networks of younger non-Hispanic black men who have sex with men. The high level of geographic heterogeneity observed suggests that HIV prevention programs should be targeted toward networks of younger people rather than geographic areas of high incidence. This study could also guide prevention efforts in other diverse metropolitan regions with characteristics similar to those of Chicago.

Keywords: HIV; MSM; networks.

Figure 1.

Region of residence (north, south, and west) in Chicago, Illinois, defined by ZIP code at the time of human immunodeficiency virus (HIV) diagnosis for a sample of 1154 people: Variant, Atypical, and Resistant HIV Surveillance system, 2005-2011. People with a ZIP code not in one of these regions were classified as “other.” Source of data on regions of residence: City of Chicago.

Figure 2.

Inferred human immunodeficiency virus (HIV) transmission network among people in clusters (15.3% of total people with sequences) in Chicago, Illinois, 2005-2011: A, race/ethnicity; B, self-reported transmission; C, region of residence at HIV diagnosis. Edge connection between nodes represents an inferred potential transmission between people, as assessed through phylogenetic analyses of the pol region with a maximum genetic distance of 1.5% (n = 1154). Figures created by NodeXL, version 1.0.1.340 (Social Media Research Foundation). Abbreviations: MSM, men who have sex with men; PWID, person who injects drugs.