Syphilis and HIV infection among rapid testing users, RJ/Brazil

Spontaneous demand for sexually transmitted infection (STI) testing represents an important entry point for prevention and early diagnosis, particularly in socially vulnerable populations. However, the sociodemographic and behavioral characteristics of individuals seeking testing remain underexplored in many regional settings.To investigate the seroepidemiological profile and associated behavioral and sociodemographic factors among individuals undergoing rapid testing for syphilis and HIV in a spontaneous-demand setting. This observational, cross-sectional, prospective study was conducted between October 2022 and July 2025 at the Clinical Analysis Laboratory of Fluminense Federal University (LAC-UFF), Brazil. A total of 300 individuals were interviewed using standardized questionnaires addressing sociodemographic characteristics, substance use, sexual behavior, and preventive practices. Rapid tests for syphilis and HIV were performed, and reactive syphilis results were confirmed by VDRL. Descriptive and bivariate analyses were conducted. Participants ranged from 18 to 86 years (mean: 42.9 years). Women predominated (57.3%), and most individuals reported low household income (71.7%). Reactive results were observed in 4.67% for syphilis rapid tests, 2% for VDRL, and 0.67% for HIV. Older age was significantly associated with syphilis infection (p = 0.0044). Younger age was associated with illicit drug use, cannabis consumption, and alcohol use. Substance use was more frequent among low-income individuals and was associated with reduced condom use. Lower income was also linked to a higher number of sexual partners and inconsistent condom use. Unprotected sexual intercourse was significantly associated with multiple partners, non-use of condoms, and single marital status (p < 0.001). Spontaneous STI testing services reach individuals with diverse but often vulnerable sociodemographic profiles. Age, socioeconomic status, substance use, and sexual behavior interact to shape syphilis and HIV risk. Integrated, intergenerational, and socially sensitive prevention strategies—combined with accessible rapid testing and confirmatory algorithms—are essential to reduce transmission and address persistent sexual health inequities.