Breaking the Chain: HIV-1 Transmission Clusters among People who Inject Drugs in North Carolina, 2010 to 2023

BACKGROUND: Injection drug use (IDU) remains a major mode of HIV transmission in the United States, with rising use putting more people who inject drugs (PWID) at risk for HIV. Understanding HIV transmission clusters in this population can inform public health outreach strategies. We examined factors associated with linkage to HIV clusters among PWID in North Carolina (NC). SETTING: NC maintains a statewide molecular HIV surveillance system, enabling identification of transmission clusters across diverse urban and rural communities. METHODS: We analyzed data from people ≥13 years old, diagnosed with HIV, residing in NC, with ≥1 HIV sequence collected between April 2010 and March 2023. Genetic clusters were defined as ≥2 sequences with a pairwise genetic distance <1.5%. Poisson regression was used to estimate prevalence ratios for factors associated with cluster linkage. A logistic generalized additive model was then used to analyze the trend in cluster linkage among PWID over time. RESULTS: Among 21,245 people with a sequence, 1,526 clusters were identified; 284 (19%) included ≥1 PWID (size range 2-218). Cluster linkage was associated with non-Hispanic White race/ethnicity, recent sequence collection, and factors associated with early HIV infection (high CD4 T-cell count, high viral load, and acute infection). The proportion of PWID linked to a cluster increased by year of HIV sequence collection. CONCLUSION: Early HIV testing and care are important for reducing transmission among PWID. Increased linkage of PWID to clusters likely reflects expansion of sequencing, which supports use of molecular clustering to identify groups needing additional outreach.