Identification of a Human Immunodeficiency Virus Type 1 and Neurosyphilis Cluster in Vermont

Abstract

Background: Rates of syphilis in the United States have more than doubled over the last several decades, largely among men who have sex with men (MSM). Our study characterizes a cluster of neurosyphilis cases among people with human immunodeficiency virus 1 (HIV-1) in Vermont in 2017-2018.

Methods: Vermont Department of Health disease intervention specialists conduct interviews with newly diagnosed HIV-1 cases and pursue sexual networking analyses. Phylogenetic and network analyses of available Vermont HIV-1 polymerase (pol) sequences identified clusters of infection. Fishers-exact and independent t-tests were used to compare people with HIV-1 within or outside an identified cluster.

Results: Between 1 January 2017 and 31 December 2018, 38 residents were diagnosed with HIV-1 infection. The mean age was 35.5 years, 79% were male and 82% were White. Risk factors for HIV-1 included MSM status (79%) and methamphetamine use (21%). Eighteen cases (49%) had HIV-1 viral loads (VLs) >100 000 copies/mL and 47% had CD4 cell counts <200/mm3. Eleven of the 38 (29%) had positive syphilis serology, including four (36%) with neurosyphilis. Sexual networking analysis revealed a ten-person cluster with higher VLs at diagnosis (90% with VLs > 100 000 copies/mL vs 33%, P = 0.015). Phylogenetic analysis of pol sequences showed a cluster of 14 cases with sequences that shared 98%-100% HIV-1 nucleotide identity.

Conclusions: This investigation of newly infected HIV-1 cases in Vermont led to identification of a cluster that appeared more likely to have advanced HIV-1 disease and neurosyphilis, supported by phylogenetic and network analyses.

Keywords: HIV-1; neurosyphilis; syphilis.

Figure 1.

Number of individuals living with HIV-1 with or without concomitant syphilis in 2017–2018, by month. Abbreviations: HIV-1, human immunodeficiency virus type 1; Neuro, neurosyphilis; Syph, syphilis.

Figure 2.

Identification of a large cluster of persons living with both human immunodeficiency virus type 1 (HIV-1) and syphilis. Phylogenetic relationships inferred with maximum likelihood analysis using HIV-1 polymerase sequences from 105 persons from Vermont, 100 reference sequences identified at GenBank, and 3 subtype J reference sequences. Shimodaira–Hasegawa probabilities >0.8 are provided at phylogenetic tree nodes. Cases in the 14-member cluster with syphilis diagnoses are in blue text and tree branches. Large Vermont (green), reference (gray), and mixed clades (white) are collapsed as triangles for clarity. Number of clade taxa are provided in parentheses. Scale bar indicates number of nucleotide substitutions per site. Abbreviation: VT, Vermont.

Figure 3.

HIV-1 genetic and contact tracing networks of a large 14-member cluster. HIV-1 polymerase sequences and associated epidemiologic data were combined and visualized using MicrobeTrace. A genetic distance cutoff of 1.5% was used to infer the genetic network that was then filtered using a nearest neighbor algorithm in MicrobeTrace. Network linkages with only either HIV-1 genetic links or contact tracing links are indicated with dark and light blue lines, respectively. Dashed blue lines indicate both a reported contact tracing and HIV-1 genetic link. Circles and squares represent cases diagnosed with and without syphilis infection, respectively. Cases that reported using and not using methamphetamine are indicated in the network with purple and green nodes, respectively. Abbreviations: DIS, disease intervention specialist; HIV-1, human immunodeficiency virus type 1; meth, methamphetamine.