Abstract
Hepatitis delta virus (HDV) is the most aggressive form of chronic viral hepatitis, yet substantial knowledge gaps exist regarding its epidemiology and optimal diagnostic workflows. From February 2019 to March 2022, an HBV screening project was conducted across various healthcare settings in Valencia, Spain. This included twenty-six primary care centers, six sexual and reproductive health centers, three mental health centers, three addiction treatment centers, selected hospital departments, outpatient clinics, and a penitentiary center. A retrospective analysis of HDV diagnostic and prevalence (2007-2020) was followed by prospective HDV screening using reflex testing from April to October 2022. Of 31,995 patients screened, 141 were HBsAg-positive (0.44% seroprevalence). Previously unknown HBV infection prevalence was 0.36%. Among HBsAg-positive patients, 5.15% had HDV IgG/IgM antibodies, and 2% had HDV RNA. Reflex single-step HDV testing increased HDV diagnosis coverage from 24 to 99.4%. This study highlights the effectiveness of reflex HDV testing, which significantly increased diagnostic coverage and simplified the screening process. Reflex testing provides a cost-effective and efficient approach, particularly benefiting high-risk populations such as migrants, who accounted for 77.8% of HBsAg-positive cases. Its implementation is crucial for improving patient outcomes and addressing gaps in HDV diagnosis and management.