Distribution of HIV-1 subtypes and molecular transmission networks among HIV/AIDS cases in Dinghai District, Zhoushan, China

This study examined the molecular transmission characteristics of human immunodeficiency virus type 1 (HIV-1) among newly diagnosed HIV/acquired immunodeficiency syndrome cases in Dinghai District, Zhoushan City, Zhejiang Province, with the aim of informing targeted prevention and control strategies. Newly reported HIV/acquired immunodeficiency syndrome cases from 2022 to 2024 were enrolled, and demographic as well as epidemiological information was collected. Plasma samples obtained prior to antiretroviral therapy were subjected to reverse transcription and nested polymerase chain reaction to amplify the polymerase gene. HIV-1 subtypes were determined using Neighbor-Joining phylogenetic analysis, and molecular transmission networks were constructed with Cytoscape 3.6.1 based on Tamura-Nei 1993 (model) genetic-distance thresholds. A total of 147 cases were identified during the study period, among which 121 blood samples were collected and 117 high-quality polymerase gene sequences were successfully obtained. Of these cases, 87.18% were male, 46.15% were aged ≥50 years, and 71.79% had a junior high school education or below. Commercial heterosexual contact was the most frequently reported route of transmission (38.46%). Thirteen HIV-1 subtypes were identified with CRF07_BC (37.61%) and CRF01_AE (23.93%), being the predominant strains. Using a genetic-distance threshold of 1%, 14 molecular clusters comprising 36 sequences were identified, corresponding to an overall clustering rate of 30.77%. The largest cluster included 10 individuals. Notably, 9 high-risk individuals with 4 or more network links were all infected with CRF07_BC and were predominantly older males with lower educational levels who reported commercial heterosexual exposure. In conclusion, CRF07_BC and CRF01_AE were the dominant HIV-1 subtypes circulating in Dinghai District. Middle-aged and older individuals involved in commercial heterosexual activities constituted the core of the local transmission network. Strengthening targeted interventions and expanding HIV testing coverage in this population are essential to prevent further transmission. These findings indicate that molecular transmission-network analysis can provide useful district-level evidence for identifying potential priority populations and optimizing targeted HIV prevention strategies in Dinghai District. The group with higher clustering signals may play an important role in local transmission, but molecular links should not be interpreted as proof of direct transmission.