Identification of occult hepatitis B virus infection in blood donors with non-discriminated reactive in southwest China

Background: Since 2011, Chongqing Blood Center began routine screening of viral nucleic acid using a multiplex assay for simultaneous detection of HBV DNA, HCV RNA and HIV-1 RNA in blood donations. However, this multiplex nucleic acid testing (NAT) screening system introduced an intractable problem of non-discriminated reactive (NDR) donations, which were serologically nonreactive and reactive in multiplex NAT screening, but nonreactive in the following virus-specific discriminatory NAT assays. Some donations were considered to arise from the presence of low-level HBV DNA due to occult hepatitis B infection (OBI). We identified OBI among NDR donations in Chongqing area. In addition, rationality of the current blood screening strategy was evaluated. Methods From August 2017 to July 2018, 190 NDR blood donations were collected from 140577 volunteer blood donors at Chongqing Blood Center. Repeated discriminatory HBV (dHBV) testing, minipools-NAT (MPs-NAT), quantitative viral load determination and complementary serological testing were used to confirm OBI. Results Of 190 NDR donations, sixty-three (33.2%) were identified as OBI, sixty-one (32.1%) were repeatedly reactive in discriminatory HBV assay. Two (1.1%) were positive for HBV DNA in MPX assay on Roche Cobas s201 system. Of these sixty-three OBI donations, only thirteen (20.6%) were positive in Cobas AmpliPrep/TaqMan HBV DNA quantitative assay, which were all less than 20IU/ml. Anti-HBc and anti-HBs were detected in 85.3% and 58.4% of NDR donors, respectively. Anti-HBc and anti-HBs were detected in 96.8% and 47.6% of confirmed OBI donors in NDR group, respectively. Anti-HBc and anti-HBs were detected in 79.5% and 63.8% of unclassified donors in NDR group, respectively. There was no statistical difference in positive rate of anti-HBc between NDR donations and dHBV-initially-reactive donations (85.3% vs 90.0%). The male to female ratio was 2.2 of OBI donors in NDR group. The proportion of repeat-time OBI donors in NDR group was higher than that in dHBV-initially-reactive group (63.5% vs 50.0%). The median age of OBI donors was 45 years in NDR group. Conclusion A complicated OBI confirmatory procedure with labour-intensive and sophisticated equipment was implemented successfully. OBI with extremely low virus concentration is the main reason for discriminatory NAT nonreactive among blood donors in Chongqing area. The current blood screening strategy is a reasonable measure to reduce the risk of transfusion, which is able to maximize blood safety.