A method for estimating the residual risk of transfusion‐transmitted HBV infection associated with occult hepatitis B virus infection in a donor population without universal anti‐ HB c screening

Background and Objectives This report describes a method for estimating the risk of transfusion‐transmitted HBV infection attributable to blood components from donors with occult hepatitis B virus infection ( OBI ) applicable where universal anti‐ HB c screening is not performed. Materials and Methods In the context of parallel HB sAg and individual donation HBV DNA testing, we developed a mathematical function p( OBI ) to estimate the probability of failing to detect [ p( NAT nondetection)] a potentially infectious [ p(transmission)] donation from a donor with OBI . Results Among 1 312 451 donations tested for HBsAg and HBV DNA, 29 (from 17 anti‐HBc reactive donors classified as OBI) were individual donation NAT negative, giving a p(NAT nondetection) of 2·2096 (95 CI: 1·538–3·173) × 10 −5 . To date, lookback on OBI donors has identified 35 (8·2%) recipients with evidence of current or past HBV infection among 427 tested recipients. After correcting for the background anti‐HBc rate in recipients, this results in a p(transmission) of 0·0384 (0·0167–0·0601). The product, pOBI is 1 in 981 920 (95% CI: 437 181–3 223 701). When this is summed with the WP risk for the 2011–2012 period, the overall HBV residual risk estimate is 1 in 538 224 (95% CI: 209 732–1 552 443). Conclusion We estimate the OBI residual risk in Australia is approximately 1 in 982 000 per unit transfused, and this risk represents 55% of the total HBV residual risk and is declining as consequence of ID ‐ NAT identifying repeat donors with OBI .