Absence of Detectable Anti-HDV Antibodies Among HBsAg-Positive Blood Donors, HIV-Infected Individuals and Patients With Chronic Hepatitis B in Sao Paulo, Brazil: Evaluation Using a Rapid Lateral Flow Assay.

Hepatitis Delta Virus (HDV) infection in HBV-infected individuals is associated with severe clinical outcomes, and screening is recommended in HBsAg-positive patients. We used a rapid lateral flow assay (LFA) to assess anti-HDV antibodies in Brazil, where HDV is highly endemic in the North, while data from the Southeast, particularly São Paulo, remain limited. We conducted a retrospective cross-sectional study to assess anti-HDV antibodies among 46 HBsAg-positive blood donors at Fundação Pró-Sangue/Hemocentro de São Paulo, 381 patients with chronic hepatitis B from the Central Laboratory Division of HC-FMUSP, and 189 individuals from the Hepatology Clinic of HC-FMUSP (101 HIV-infected and 88 chronically HBV-infected). Anti-HDV antibodies were detected using a validated LFA. Positive controls (n = 24) included samples previously confirmed by ELISA and/or PCR, predominantly infected with HDV genotypes 3 and 8. Among 443,400 blood donations, 48 (0.01%) were positive for at least two HBV markers; of these, 46 were tested for HDV, and all were anti-HDV negative. All 381 patients undergoing HBV viral load monitoring were anti-HDV negative, as were all 189 patients receiving hepatology care, including those with HIV coinfection or advanced liver disease. The LFA correctly identified all control samples positive for both anti-HDV antibodies and HDV RNA. The absence of detectable anti-HDV among diverse at-risk populations in São Paulo is consistent with the low endemicity of HDV infection in southeastern Brazil. These findings, together with the assay's high specificity in HDV RNA-positive controls, support its potential utility as a screening tool for HDV infection in low-prevalence settings.