Assessment of the effectiveness of West Nile virus screening by analysing suspected positive donations among blood donors, Germany, 2020 to 2023
Stefano Orru', Annette Reissinger, Angela Filomena, Anna Heitmann, Markus Benedikt Funk, Jonas Schmidt-Chanasit, Julia Kreß, Heinrich Scheiblauer, Dániel Cadar, Sarah Anna FiedlerBackground
The first autochthonous human West Nile virus (WNV)-positive cases in Germany were confirmed in 2019. Risk minimisation measures (RMM) were introduced in 2020; no WNV transfusion-transmitted infections have been reported to date.
Aim
To analyse German suspected WNV-positive blood donations during annual seasons 2020–23 to review donor testing requirements.
Methods
WNV look-back procedures were initiated as per German regulations and additional donor data were collected. Blood samples were analysed by metagenomic next-generation sequencing (mNGS), individual donor nucleic acid amplification technique (ID-NAT)-based testing and antibody (Ab) testing.
Results
Seventy-four cases were followed up after WNV-positive donor mini-pool screening. Forty-five (83%) of 54 samples tested with the cobas WNV assay and 14 (29%) of 49 samples tested with the RealStar WNV assay showed a reactive ID-NAT-based result; the viral load ranged between 70,251 IU/mL and values below quantification limits. Fifteen (23%) of 64 samples serologically tested were reactive with at least one of the three Ab tests performed; the previous WNV-negative donation was nearly always documented > 28 days before. Of 73 samples sequenced, mNGS detected WNV in 26 (36%) and other flaviviruses in 14 (19%) cases.
Conclusion
In some suspected cases where a WNV infection was not confirmed, mNGS demonstrated a cross-reaction with other flaviviruses. Ab testing could only detect WNV in late stages of infection. A NAT-based WNV donor screening with a detection limit of at least 120 IU/mL seems to be a sufficiently effective RMM at present. However, a continuous re-evaluation of test strategy is always required.