HIV prevalence among adults in Chad is estimated at 1.2%, with serodiscordant couples representing a key population in efforts to control the national HIV epidemic. This study assessed the relationship between plasma and genital HIV-1 RNA loads and their impact on sexual transmission, alongside the prevalence and transmission dynamics of sexually transmitted infections (STIs), including hepatitis B virus (HBV), hepatitis C virus (HCV), and syphilis within these couples. HIV-1 RNA was extracted from genital secretions using the QIAamp Viral RNA Mini Kit and quantified on the MIC platform, while plasma viral loads were measured using the automated GeneXpert system. Rapid diagnostic tests were used for HBV surface antigen, HCV antibodies, and syphilis antibodies screening. Among HIV-positive partners, 68.4% had undetectable plasma viral loads (<40 copies/mL), 15.8% had low-level viremia (41–600 copies/mL), and 15.8% had high viral replication (>1000 copies/mL). Viral RNA was undetectable in genital secretions in 84.2% of cases; the remainder exhibited low-level shedding (median 308.5 copies/mL). A strong positive correlation was observed between plasma and genital viral loads (r = 0.894, p = 0.001). Co-infections were identified in 2.6% (HCV), 15.8% (HBV), and 11.8% (syphilis), with transmission rates of 0%, 50%, and 100%, respectively. These findings show that while HBV and syphilis transmit efficiently between partners, effective antiretroviral therapy suppresses HIV replication in plasma and genital secretions, preventing HIV transmission within serodiscordant couples. Continued monitoring and management of co-infections remain essential to support prevention efforts in this population.

HIV-1, plasma/genital viral load, sexually transmitted infections (STIs), serodiscordant couples, Chad