Characterization of occult hepatitis B virus strains in south african blood donors

Since October 2005, all blood units collected in South Africa were screened individually for human immunodeficiency virus (HIV)‐1, hepatitis B and C virus (HBV, HCV) genomes uncovering preseroconversion window period (WP) infections for each virus and occult HBV infections (OBIs) defined as persistent HBV DNA without detectable hepatitis B surface antigen (HBsAg). Samples identified as HBsAg‐negative/DNA‐positive were confirmed by combining real‐time quantitative polymerase chain reaction, nested amplification, anti‐HBc and anti‐HBs. Amplified basic core promoter/precore, pre‐S/S, and whole genome were sequenced, analyzed, and compared to 73 HBsAg+ strains. Genotype was determined by phylogenetic analysis. From 109 samples examined, 54 were classified as OBI, 14 as WP, 20 as false‐positive, five as other classification, and 16 as undetermined due to lack of serological or follow‐up data. OBI donors were predominantly males (67%), median age 31 years, black (54%), with normal alanine aminotransferase levels. Viral load ranged between unquantifiable and 518 IU/mL (median 5 IU/mL). Genotype A1 was more frequent (23 strains) than genotype D (seven strains). Genotype A1 strains were little mutated. In the major hydrophilic region, 56.5% strains were wild type or with few amino acid substitutions. Most important, all 13 full genome sequences presented 1 to 7 mutations known to or assumed to negatively impact viral replication. In particular, 6/13 sequences had a stop codon in the HBx gene translated into deletion of 117 or 19‐25 C‐terminus amino acids not found in 15 HBeAg+ HBsAg+ strains. One WP sequence with an HBx stop codon suggested infectivity. Conclusion: Genotype A1 OBIs are different from genotype A2 and D OBIs in that there is little evidence of immune pressure as a major factor involved in OBI genesis. Limited replication appears mostly related to genetic viral defects. (HEPATOLOGY 2009.)