Primers and probes used for HBV DNA detection.

<div><p>Background</p><p>Occult hepatitis B infection (OBI) is characterized by the presence of hepatitis B virus (HBV) DNA at low levels in serum (<200 IU/mL) with a negative hepatitis B surface antigen (HBsAg) test. OBI remains a major challenge to blood safety, particularly in HBV-endemic regions like Cameroon, where HBV detection relies solely on HBsAg testing. This cross-sectional study aimed to investigate the actual incidence and genotype characteristics of OBI in Cameroonian blood donors.</p><p>Methods</p><p>Between March and June 2023, samples were collected from 288 HBsAg-negative blood donors aged 18 to 55 years and analysed for antibodies against the HBV core (anti-HBc) and surface antigens (anti-HBs). Following DNA extraction from the serum samples, qualitative nested PCR and quantitative real-time PCR were used to detect HBV viral DNA and viral load respectively. For positive samples, sequencing of a fragment of the <i>S</i> gene was performed to identify the circulating HBV genotypes.</p><p>Results</p><p>The findings revealed that 58% (n = 167/288) of blood donors tested positive for anti-HBc, 29% (n = 83/288) tested positive for anti-HBs, and 26% (n = 75/288) being positive for both anti-HBc and anti-HBs. Occult hepatitis was confirmed in 4.5% of the blood donors, all of whom belonged to either HBV genotypes <i>A</i> or <i>E</i>, which are predominant in Cameroon. The amino acid substitution <i>sA184V</i> associated with HBsAg detection failure in genotype E was observed in 70% of OBI sequences, and the HBsAg immune escape variants (s<i>T131N</i> and s<i>S143L</i>) implicated in OBI were also observed. The mutation <i>rtN139K</i> in the reverse transcriptase (RT) domain of the overlapping HBV polymerase (<i>P</i>) gene was present in 17% of OBI-positive sequences of genotype <i>E</i>, likely contributing to masking HBsAg secretion.</p><p>Conclusion</p><p>The results suggest a considerable risk of transfusion-transmitted HBV in this region. Therefore, to ensure blood safety, nucleic acid testing (NAT) is recommended, as relying solely on HBsAg assays is insufficient to eliminate this risk.</p></div>