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-HBc screening.

ABSTRACT

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-HBc screening is not performed. MATERIALS AND METHODS: In the context of parallel HBsAg 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.