Evidence of acute primary occult hepatitis B virus infection in an Italian repeat blood donor.

BACKGROUND: Preliminary evidence of cases of acute occult hepatitis B virus (HBV) infection (OBI) has been recently reported in the literature. Furthermore, OBI definition has been the object of an international consensus conference. STUDY DESIGN AND METHODS: A case of acute primary OBI was identified and followed up in a repeat female blood donor using a highly sensitive nucleic acid test (NAT; Procleix Ultrio on Tigris, Chiron). Genotyping and sequencing of virus isolates from donor and contact cases were performed. RESULTS: The blood donor never developed detectable hepatitis B surface antigen (HBsAg) until seroconversion to antibody to hepatitis B surface antigen/antibody to hepatitis B core antigen. A very low viral load was observed during the infection course (<50 IU/mL). Donor HBV DNA sequencing consistently showed a CCA deletion leading to amino acid T116 deletion in the small envelope protein (S). Other sequence features showed high homology between donor and contact case, suggesting a sexual transmission. DISCUSSION: The main explanation for HBsAg undetectability relies on the very low level of viremia observed. The single-amino-acid deletion found in the S protein cannot account for HBsAg detection failure, because the capture antibody of the assay used is targeted to a different sequence epitope (aa121-124). Meanwhile, CCA deletion may have impacted the virus replication efficiency since it affects the overlapping reverse transcriptase "finger" domain of the polymerase gene. These findings define this case as an acute primary OBI, confirming the existence of this condition. NAT with high sensitivity is the only screening enabling prevention of HBV transmission by transfusion in such cases.

Italian blood donors with anti-HBc and occult hepatitis B virus infection.

BACKGROUND AND OBJECTIVES: Occult hepatitis B virus (HBV) infection might allow the release of viremic units into the blood supply network if blood is tested only for hepatitis B surface antigen (HBsAg). The aim of our study was to evaluate the actual prevalence, viral load and genotype of occult HBV infections among first-time blood donors in north-western Italy and to suggest a way to minimize risks of transmission of this infection. DESIGN AND METHODS: We assayed 6313 consecutive blood donors for antibodies to HBV core antigen (anti-HBc) in addition to mandatory screening. HBsAg-negative/anti-HBc-positive donors were assayed for antibodies to HBsAg (anti-HBs) and for HBV-DNA using COBAS Ampliscreen HBV (Roche) on individual donations. All HBV-DNA-positive samples underwent confirmatory testing with additional polymerase chain reaction-based assays. RESULTS: The prevalence of anti-HBc positive subjects was 4.85%. Fourteen out of 288 blood donors (4.86%) were confirmed to have circulating HBV-DNA at a low level (range 8-108 IU/mL). All viremic donors were also anti-HBs-positive. INTERPRETATION AND CONCLUSIONS: We estimate that in north-western Italy up to 2298 units per million donated units from first-time donors may contain HBV-DNA. The risk of an HBV-DNA positive unit from an occult carrier being released into the blood supply is more than 100 times higher than the estimated residual risk related to the window phase of HBV infection in our country. The potential infectivity of these units is debated, but their use cannot be considered safe at least in immunocompromised patients.