Dynamics of clustering rates in the rhode Island HIV-1 epidemic.

Background: : Characterizing HIV clustering rates and their trends over time can improve understanding a local epidemic and enhance its control.

Methods: Leveraging an academic-public health partnership in Rhode-Island, we explored longitudinal dynamics of statewide clustering rates among key populations from 1991 to 2023. Partial HIV-1 pol sequences were grouped by year of HIV-1 diagnosis. Molecular clusters were identified in cumulative annual phylogenies. Overall clustering rates, and clustering rates of newly-diagnosed and prevalent infections, and of specific socio-demographic characteristics of key populations over time were determined. Mann-Kendall statistics were used to estimate clustering rate trends and relationships among groups.

Results: By the end of 2023, 2,630 individuals with sequences represented the statewide epidemic in Rhode Island. Overall clustering rates increased from 7% in 1991 to 46% in 2023, correlating with cumulative sequence increase. Clustering rates of newly-diagnosed and prevalent infections significantly increased over time, higher in newly-diagnosed individuals since the early 2000 s. Increases were also observed among groups defined by gender, age, transmission risks, race, mental illness, HIV-1 subtypes, and country of birth, with some crossovers and divergence patterns over time.

Conclusions: Exploring dynamics of HIV clustering rates over three decades in a statewide HIV-1 epidemic expanded its characterization and provided insight into its evolving changes. These dynamics may indicate a gradual shift towards a more concentrated and localized HIV-1 epidemic, highlighting important opportunities for targeted interventions to effectively prevent new HIV transmissions.