HDV seroprevalence in Germany. (A) Databank research of HBsAg-positive patients. Diagnostic testing data from 1628 HBsAg-positive patients that were admitted to the University Hospital Heidelberg between 2014 and 2019 were evaluated to determine the anti-HDV-Ab, anti-HCV, and anti-HIV 1/2 testing rates. (B) Testing for anti-HDV-Ab in HBsAg-positive patients. A total of 684 sera from HBsAg carriers admitted to the University Hospital Heidelberg between 2014 and 2019 with uncharacterized anti-HDV-Ab status were retrospectively tested for anti-HDV-Ab using the HDV rapid test. NA: samples for which no databank serum was available. (C) Validation of anti-HDV-Ab positivity. Sera that tested anti-HDV-Ab-positive using the HDV rapid test were re-tested using a standard, semi-quantitative in-house ELISA. Averaged results from three independent experiments are shown. (D) Testing for anti-HDV-Ab in 263 HBsAg-negative, anti-HBc-negative, anti-HCV-positive patients that were admitted to the University Hospital Heidelberg in 2019. Sera were tested for anti-HDV-Ab using an in-house ELISA. The averages of triplicate results at 1:100 dilutions are shown. Blue: sera showed equivocal ELISA signals >1.5-fold of the negative patient serum. (E) Re-evaluation of patient sera with equivocal anti-HDV-Ab testing results using a semi-quantitative in-house ELISA.