Seroepidemiological Prevalence of Hepatitis B and C Virus Coinfection: A Large-Scale Retrospective Cohort Study in Istanbul.

Background/Objectives: Hepatitis B (HBV) and hepatitis C (HCV) coinfection leads to the progression of liver disease and results in clinically serious outcomes. Continuous monitoring of epidemiological data is crucial for managing the regional disease burden. This study investigates the current seroprevalence of HBV and HCV, the prevalence of coinfection, and the rates of active replication in Istanbul. Methods: This retrospective analysis included 7131 patients evaluated at the Infectious Diseases and Gastroenterohepatology clinics between 2021 and 2025. Initial serological screening for viral markers was performed using routine chemiluminescent immunoassays. Active viral replication was subsequently confirmed and quantified via real-time polymerase chain reaction (PCR). Results: Active HBV replication was significantly more frequent among patients in the Gastroenterohepatology clinic (20.47%) compared to those in Infectious Diseases (5.36%). Active HCV infections were rare in both departments (0.25% and 0.04%, respectively). Simultaneous HBV and HCV coinfection was detected in only 17 patients (0.24%). Demographic evaluation demonstrated that HBV marker positivity was more prevalent in male patients and individuals over 40 years of age. Conclusions: HBV seroprevalence remains substantially higher than HCV in this cohort. The high rate of active HBV replication in gastroenterohepatology settings indicates a concentrated burden of active disease in these specialized clinics. These distribution patterns emphasize the necessity of routine, targeted HBV screening for older male demographics to facilitate early clinical intervention.