Molecular transmission network analysis of HIV-1 among older adults in Central China: a cross-sectional study in Shaodong City.

Objective: The ageing population poses emerging challenges to HIV prevention, particularly in regions with high proportions of older adults. We conducted a cross-sectional study of 513 newly diagnosed HIV-infected individuals in Shaodong City, Hunan Province, China, between 2021 and 2025, with a focus on individuals aged ≥60 years. Methods: HIV-1 pol sequences were amplified, sequenced, and analyzed for subtype distribution and transmitted drug resistance (TDR). Molecular transmission networks were constructed using a 0.5% genetic distance threshold, and clusters were classified as large (≥10 nodes), medium (5-9 nodes), or small (<5 nodes). Results: CRF85_BC was the predominant subtype (32.55%), and a total of 37 transmission clusters were identified, with the two largest clusters comprising 99 and 19 nodes, respectively. High-risk nodes, defined as those with a transmission network score (TNS) ≥ 0.75 and degree ≥4, were primarily older male farmers engaged in heterosexual commercial sex. The overall TDR prevalence was 10.53%, with NNRTI resistance predominating, and K103N being the most frequent mutation. Conclusion: Our findings indicate that HIV transmission among older adults exhibits substantial clustering, largely driven by commercial sexual activity, and highlight the importance of molecular network analysis for identifying high-risk individuals and guiding targeted prevention interventions. Continuous surveillance of TDR within active clusters is critical for optimizing antiretroviral therapy strategies and mitigating onward transmission.