Identification of an HIV-1 and Neurosyphilis Cluster in Vermont.

Background Rates of syphilis in the U.S. 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 HIV-1-infected individuals in Vermont in 2017-2018. Methods Vermont Department of Health disease intervention specialists conduct interviews with all newly diagnosed HIV-1 cases and pursued 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 HIV-1-infected individuals within or outside an identified cluster. Results Between January 1, 2017 and December 31, 2018, 38 Vermont residents were newly diagnosed with HIV-1 infection. The mean age was 35.5 years, 79% were male and 82% were white. Risk factors for HIV-1 acquisition 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 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. Identification of a cluster was strongly supported by both phylogenetic and network analyses of HIV-1 pol sequences.