Characterization of occult hepatitis B virus from blood donors carrying genotype A2 or genotype D strains

Background/Aims Nucleic acid testing (NAT) for hepatitis B virus (HBV) DNA in blood donations identified occult HBV infection (OBI) as a potential threat to blood safety. Methods A collaborative study was undertaken to explore the molecular basis of OBIs prevalent in Europe in relation to clinical and serological data. Results Ninety-one percent of 77 donor samples of European origin HBV DNA positive but HBV surface antigen (HBsAg) negative were confirmed. Viral load ranged between unquantifiable and 5640IU/mL (median 25IU/mL). Fifty-two strains were genotyped (14 HBV A2 and 38 HBV D ). Compared to HBsAg+ samples, genotype D was significantly more frequent than genotype A2 in OBIs from Poland or Italy ( P P P P P P Conclusions Results support the hypothesis that humoral and cellular immune pressure on the HBV envelope proteins are major mechanisms generating OBI.