Marked reduction in the incidence of transfusion‐transmitted hepatitis B virus infection after the introduction of antibody to hepatitis B core antigen and individual donation nucleic acid amplification screening in Japan

Background In Japan, 41 million blood donations have been screened for hepatitis B virus (HBV) during the past 8.4 years using individual donation nucleic acid amplification testing (ID‐NAT) and antibody to hepatitis B core antigen (anti‐HBc) screening. Study Design and Methods Transfusion‐transmitted HBV infection (TT‐HBV) incidence was examined. Donated blood implicated in TT‐HBV was analyzed for infection stage and DNA levels. Causative HBV strains were phylogenetically analyzed. Results Among 5162 (0.013%) ID‐NAT positives, window period (WP) and occult HBV infection (OBI) accounted for 3.4% (176) and 11.5% (594), respectively. No OBI‐related TT‐HBV occurred. Seven blood donations caused eight TT‐HBV cases, six of which were in the pre‐ID‐NAT WP, leaving one with an unresolved infection stage. Seven cases were caused by platelet concentrate (180 mL plasma) and one case by fresh‐frozen plasma (200 mL plasma), which contained estimated infectious doses varying between 2 and 2300 HBV virions. HBV subgenotypes in five cases were HBV/A2. Complete genome sequences of the transmitting A2 strains were nearly identical (99.6%–100%) and clustered in a group that included HBV/HIV‐1 coinfections and a higher proportion of donors in the acute infection phase (69%) than the other group of HBV/A2 sequences (5%). Discussion The incidence of observed TT‐HBV cases has significantly reduced to 0.19 per million in the ID‐NAT screening period. OBI‐related TT‐HBV was eliminated by anti‐HBc screening. Established TT‐HBV cases were caused by blood products with large plasma volumes containing extremely low HBV concentrations derived from blood donors at a very early infection stage.