Valencia, JorgeRyan, PabloCodina Márquez, HelenaCuevas, GuillermoManzano, SamuelEstévez, SamuelMartinez, IsidoroSepulveda-Crespo, DanielResino, Salvador2026-06-262026-06-262026-06Valencia J, Ryan P, Codina H, Cuevas G, Manzano S, Estévez S, Martínez I, Sepúlveda-Crespo D, Resino S. HIV/HCV prevalence and the retention paradox in marginalized populations in Madrid (2019-2023): A large-scale cross-sectional study. Int J Infect Dis. 2026 Jun;167:108582. doi: 10.1016/j.ijid.2026.108582. Epub 2026 Mar 20. PMID: 41866060.https://hdl.handle.net/20.500.12105/27569Objectives: Marginalized urban populations experience a high burden of HIV and HCV. We assessed the prevalence and risk factors for both infections and characterized the care cascades in a cohort of vulnerable individuals in Madrid, Spain. Methods: We conducted a cross-sectional study (2019-2023) of 4582 individuals via mobile units in high-risk hotspots, offering integrated rapid HIV/HCV testing with point-of-care HCV-RNA confirmation. Multivariable logistic regression identified independent HIV risk factors. Results: HIV prevalence was 6.3% (95% CI: 5.6-7.0). Among people with HIV (PWH), 17.0% of known cases were not receiving antiretroviral therapy; PrEP uptake was zero among HIV-negative individuals. A history of injecting drug use was the primary HIV risk factor (adjusted odds ratio[aOR] 6.6; 95% CI: 4.6-9.5), followed by age >50 years, Spanish origin, and alcohol/benzodiazepine misuse (all P < 0.05). Active HCV prevalence was 5.5% (95% CI: 4.9-6.2); 15.7% in PWH vs 4.8% in people without HIV (P < 0.001). Among confirmed cases, HCV linkage (≥95.2%) and treatment (≥88.6%) were high; however, 16.8% of all antibody-positive individuals (23.2% among PWH) missed confirmatory RNA testing. Conclusions: HIV and HCV remain prevalent, characterized by discontinuities in retention rather than diagnosis. Integrated, low-threshold strategies combining harm reduction with social support are required to address this syndemic.engVoRhttp://creativecommons.org/licenses/by/4.0/HIVHIV/HCV coinfectionLink to careScreeningVulnerable populationsAdultCoinfectionCross-Sectional StudiesFemaleHIV InfectionsHepacivirusHepatitis CHumansMaleMiddle AgedPrevalenceRisk FactorsSpainSubstance Abuse, IntravenousVulnerable PopulationsAttribution 4.0 International4186606016710858210.1016/j.ijid.2026.108582International Journal of Infectious Diseasesopen access