Detection and identification of occult hepatitis B virus infection among blood donors

Abstract

Background: Occult hepatitis B virus infection (OBI) is defined as the presence of circulating hepatitis B virus (HBV) DNA as detected by HBV nucleic acid test (NAT), in the absence of detectable HBV surface antigen (HBsAg), with or without antibodies to hepatitis B core antigen (anti-HBc) or hepatitis B surface antigen (anti-HBs). HBV infection is a continuing threat to transfusion safety, especially in developing counties like India where detection of HBV is primarily based on the screening for HBsAg as a marker of infection. Objective: To know the prevalence of OBI among blood donors and their serological and molecular characterization of NAT yield samples. Materials and Methods: A total of 41,090 blood donor’s samples from February 2014 to August 2015 were tested by individual donor-NAT (ID-NAT) apart from routine serological screening for anti-HIV 1-2, P24 antigen, anti-HCV, and Hepatitis B surface antigen (HBsAg) by Biomerieux (Vironostika® HIV Ag-Ab, Hepanostika® HCV Ultra, and HBsAg Ultra, France). All the samples were tested individually by Procleix® Utrio Plus® Assay (Novartis Emeryville, CA). Blood units that were HBsAg nonreactive but ID-NAT reactive (NAT yield) were further worked up with anti-HBc, anti-HBsAg, viral DNA load, and viral genotyping. Result: Of the 41,090 samples, 29 were reactive for HBV DNA (NAT yield). Among the 29 NAT yields, 24 were individual NAT yield, 4 were HBV–HCV NAT co-yield, and 1was HBV-HIV NAT co-yield. A total of 24 HBV individual NAT yield samples were further tested for OBI. A total of 11 samples were reactive for anti-HBc only, 3 samples carried both anti-HBc and anti-HBs, yielding a total of 14 (58.3%) samples that were classified as OBI and 1 (4.2%) sample was reactive for anti-HBs only. Nine samples (37.5%) did not have any serological marker owing to incomplete antibody, and they remained unclassified, as window period infection could not be excluded. Two HBV-NAT yield samples of genotype D, one with a window period and the second being an OBI had high viral load by qPCR. Conclusion: Blood products from donors with OBI carry a high risk of HBV transmission by transfusion. Because of multiple antigens and antibodies present in blood in response to HBV infection, at present there is no single test to detect the infection. In developing country such as India with high seroprevalence of HBV infection, combination of at least two tests would help us to improve the transfusion safety.