Triggers for switching from minipool testing by nucleic acid technology to individual‐donation nucleic acid testing for West Nile virus: Analysis of 2003 data to inform 2004 decision making

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Abstract
Concern about West Nile virus (WNV) transfusion-transmitted infections missed by minipool (MP) nucleic acid testing (NAT) has prompted consideration of the use of individual-donation (ID) NAT. Strategies were investigated for the application of limited ID-NAT capacity in 2004. Patterns of WNV MP-NAT-reactive donations tested by the Blood Systems Laboratory each week for 79 blood centers from June 29 to November 23, 2003 (196 MP-NAT repeat-reactive [RR] donations among 801,697 units), were analyzed. ID-NAT initiation strategies were developed consisting of counts of RR donations and/or weekly RR rates, together with three ID-NAT discontinuation strategies, and ID testing burden was assessed based on these combined start and stop strategies. The effectiveness, reported as the percentage of MP-RR donations that would trigger ID-NAT based on each initiation strategy, ranged from 57 to 100 percent. The addition of a 1- or 2-week no-yield requirement for ID discontinuation substantially increased testing burden. Combined strategies resulted in projected ID-NAT of between 10 and 50 percent of donations for a 10- to 20-week period. For this organization, the most feasible ID-NAT initiation strategy was 2 MP-reactive donations and a weekly rate of 1 in 1000, which had an effectiveness of 81 percent and led to peak weekly ID-NAT of 20 to 25 percent of donations depending on the discontinuation rule. This new approach of targeted ID-NAT based on ongoing monitoring of MP-NAT yield may prove to be a rational policy for agents like WNV that cause seasonal and regional epidemics.
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