Objective  To analyze the molecular network characteristics and dynamic changes of molecular clusters in HIV-infected individuals aged ≥50 years in Wenzhou, Zhejiang province, and provide evidence for the precise prevention and control of AIDS.

Methods A total of 570 plasma samples were collected from newly diagnosed HIV-infected individuals aged ≥50 years in the context of receiving no antiretroviral treatment in Wenzhou from 2022 to 2024. The pol genes were amplified with reverse transcription PCR and nested PCR, and then the nucleic acid was sequenced. Software MEGA 6.0 was used to construct a Neighbor-Joining phylogenetic tree for subtype determination. Software Cytoscape 3.9.1 was used to construct HIV molecular network.

Results A total of 528 samples were successfully sequenced. Most cases were detected in clinical consultation (42.80%,226/528) or examination before operation (28.41%, 150/528), and the proportion of the cases with CD4⁺ T lymphocyte counts below 500 cells/μL was 93.94% (496/528), below 200 cells/μL was 45.64%(241/528). Nine subtypes and unique recombinant forms were detected, CRF07_BC was the major subtype (51.33%,271/528), followed by CRF01_AE (19.32%,102/528) and CRF08_BC (9.66%,51/528). When a genetic distance threshold of 1.0% was used, a total of 230 cases were connected to the network, with a network clustering rate of 43.56% (230/528). There were 8 genotypes included in the network, and 56 molecular clusters were formed (with 2-30 nodes). The network-identified cases were predominantly local residents of Wenzhou (78.70%, 181/230) and men (76.09%, 175/230), those aged 50-<60 years (44.78%, 103/230). Most cases had educational level of primary school or below (71.30%, 164/230), and the main transmission route was heterosexual contact (88.26%, 203/230). There were significant differences in network entry status among those in different age groups (χ²=32.965,P<0.05), those living in different areas(χ²=8.667,P<0.05), those with different educational levels(χ²=17.049,P<0.05), and those with different subtypes (χ²=11.553,P<0.05). Four large clusters (C1-C4) with ≥10 nodes were all CRF07_BC. The edge/node ratios of the 4 major clusters ranged from 1.70 to 8.72, and the cases of C1-C3 were mainly in Rui'an. The number of new cases for clusters C1-C3 in 2023 and clusters C1-C2 in 2024 all exceeded 5. The Proportional Detection Rate of C1-C4 molecular networks in 2023 and 2024 ranged from 1.25 to 3.40. There were 26 cases with a degree of ≥10 in C1 and C2, in whom 69.23% (18/26) had history of non-marital sex with multiple partners.

Conclusion  HIV-1 subtypes in the infection cases aged ≥50 years in Wenzhou were diverse. The molecular network was active. Local clustered transmission was mainly driven by the CRF07_BC major cluster, and the delayed diagnosis of the cases was common. Proactive testing and health education should be strengthened in middle-aged and elderly populations in areas affected by HIV epidemic, and precise interventions should be implemented in combination with dynamic monitoring of molecular networks to reduce the sustained HIV transmission risk.