Relative distribution of West Nile virus RNA in blood compartments: implications for blood donor nucleic acid amplification technology screening

Abstract

Despite implementation of targeted individual-donor nucleic acid test (NAT) screening of blood donors for West Nile virus (WNV), three "breakthrough" WNV transfusion transmission cases were reported (2004-2008), suggesting that current plasma-based assays are unable to detect all WNV-infectious donations. A 2007 report found that 19 of 20 red blood cell components from WNV-infected donors contained 1 log higher viral load than plasma components. This study's aim was to further establish the value of screening whole blood relative to plasma for WNV RNA by generating differential viral loads on paired samples derived from blood screening tubes. WNV RNA-positive donors identified by routine NAT screening were enrolled and quantitative viral data were generated using cross-sectional (index-donation) and longitudinal (follow-up) specimens. A real-time reverse transcription-polymerase chain reaction viral load assay was used on both study sample sets and replicate qualitative NAT screening assays were also used on the longitudinal study samples. For the cross-sectional study, seronegative index donations (n = 29) had WNV RNA concentrations fourfold higher in plasma than in whole blood, whereas for seropositive donations (n = 13), the WNV RNA concentrations were 10-fold higher in whole blood than in plasma. All 10 longitudinal study participants were seropositive throughout the follow-up study; whole blood viral load was consistently greater than plasma viral load (mean difference, 343 copies; p < 0.001) up to 200 days after index. The improved sensitivity of WNV NAT using whole blood instead of plasma was confirmed, but appears to be limited to better detection in seropositive stages. However, the implication of these findings for blood screening requires further study to establish the infectivity of persistent whole blood viremia.