Resumen

Background: In late 2019, pre-exposure prophylaxis (PrEP) for HIV infection was approved in Spain, potentially altering HIV-1 molecular epidemiology and reducing the number of new infections within transmission chains (TCs). We aimed to analyze the presence and characteristics of TCs in newly diagnosed HIV-1 patients before and after PrEP implementation, and to assess the prevalence of transmitted drug resistance (TDR) to antirretroviral therapy (ART) and its association with TCs. Methods: Monocentric study, comparing new HIV-1 diagnoses before and after PrEP implementation (2016-2019 vs. 2020-2023). Sequences of HIV-1 retrotranscriptase and protease were analyzed. Phylogeny was inferred with FastTree, and subtyping with REGA and COMET. Sociodemographic, clinical, immunovirological characteristics and TDR mutations were also analysed. Statistic program: SPSS v24. Results: 456 new HIV-1 diagnoses were included. Globally, 413 (90.6%) were men, 347 (84%) having sex with men, and 300 (65.8%) Spanish, with a mean age of 43 (32-54) years; the more frequent subtypes were B (269, 59%) and CRF02_AG (29, 6.4%). Features of subjects diagnosed in the pre-PrEP and post-PrEP periods are shown in Table 1. After PrEP implementation, the percentage of MSM among all new HIV-diagnoses decreased (78.7 vs 72.5%; p=0.037), and AIDS cases increased (13.9 vs 22.8%; p= 0.014); a prior negative serology existed in 49,1% vs 53.4%, p=0.02. During pre-PrEP period, 70.9% of patients grouped in a TC vs 55% in the post-PrEP period (p=0.003). Conclusions: HIV-1 diagnoses have declined in recent years, with a decrease of MSM among all new patients and more AIDS cases after PrEP implementation. These differences in addition to a decrease in TCs suggests that PrEP may have reduced transmission within groups. TDR to NNRTIs remained stable, emphasizing the need for ongoing monitoring of resistance patterns.