Hepatitis B virus blood screening: impact of nucleic amplification technology testing implementation on identifying hepatitis B surface antigen non-reactive window period and chronic infections.

Despite improvements in hepatitis B surface antigen (HBsAg) test sensitivity, post-transfusion hepatitis B virus (HBV) infection still occurs because HBsAg is undetectable during the early window phase (WP) of the infection, in the convalescence core window phase of the infection, or in serologically silent chronic hepatitis or in mutant forms of HBV. HBV-DNA screening using high sensitivity nucleic amplification technology (NAT) assays has recently been introduced to reduce the residual risk of transmission of HBV by transfusion of blood components. Over 1 year 75 063 donations were individually screened for HBV-DNA by the Ultrio Procleix assay on the Tigris platform. The donations were collected in the Latium region, an area of the central Italy, and they accounted for the 40% of the total blood units collected in this area per year. The initial reactive samples were re-tested and confirmed by the discriminatory HBV assay. Additional HBV serological markers were also performed. Suspected WP infections were followed-up to monitor the development of the immune response. All HBV-DNA-positive donors were called back to check up their infectious status. The results of testing the 75 063 donations are: 33 donations HBsAg positive, 31 out of them HBV-DNA-positive and two HBV-DNA negative; 22 donations HBsAg-negative but HBV-DNA positive with low viral load. Six of the 22 were found to be consistently HBV-DNA reactive whereas the remaining 16 donations showed inconsistent results on multiple NAT retesting. One WP infection was confirmed by the follow-up of the donor for 3 months following the index blood donation. In the donor population of the Latium region, NAT screening has revealed a higher than expected number of donors who were HBsAg non-reactive but HBV-DNA-positive with three donors showing HBV-DNA as the only marker of infection. The adoption of genome screening has increased the safety of the blood supply and has also contributed to the protection of donor health by identifying either WP or clinically silent infections.