Assessment of the effectiveness of West Nile virus screening by analysing suspected positive donations among blood donors, Germany, 2020 to 2023

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BackgroundThe 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.AimTo analyse German suspected WNV-positive blood donations during annual seasons 2020-23 to review donor testing requirements.MethodsWNV 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.ResultsSeventy-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.ConclusionIn 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.

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