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A modeling framework for evaluation and comparison of trigger strategies for switching from minipool to individual-donation testing for West Nile virus

Authors

  • Brad J. Biggerstaff,

    1. From the Division of Vector-Borne Infectious Diseases, National Center for Zoonotic, Vector-Borne, and Enteric Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado.
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  • Lyle R. Petersen

    1. From the Division of Vector-Borne Infectious Diseases, National Center for Zoonotic, Vector-Borne, and Enteric Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado.
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  • Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention

Brad J. Biggerstaff, Centers for Disease Control and Prevention, 3150 Rampart Road, Fort Collins, CO 80521; e-mail: bbiggerstaff@cdc.gov.

Abstract

BACKGROUND: To decrease the likelihood of transmission from donations containing West Nile virus (WNV) levels below minipool nucleic acid test (MP-NAT) detection limits, blood centers switch from MP-NAT to individual-donation testing (ID-NAT) after detection of MP-NAT–positive donations. The effectiveness of strategies to trigger or discontinue ID-NAT screening is largely unknown.

STUDY DESIGN AND METHODS: Twenty-seven strategies to trigger and discontinue ID-NAT screening were evaluated with a statistical model based on known dynamics of WNV infection and historical data on WNV prevalence among blood donations. Breakthroughs were defined as WNV immunoglobulin M antibody–negative, viremic (RNA-positive) donations that could only be identified by ID-NAT, but were screened by MP-NAT. Effectiveness (proportional reduction of breakthroughs relative to MP-NAT screening alone) and efficiency (absolute reduction of breakthroughs relative to the number of tests performed) were estimated by simulating donation years of varying outbreak severities over a range of blood collection frequencies.

RESULTS: Most strategies were effective (>75% reduction in breakthroughs) when daily donations exceeded 560. In larger centers (1008 donations daily), effectiveness of trigger-on strategies based on absolute number of MP-NAT–positive donations improved, but worsened for strategies using rate-based criteria. Effectiveness increased slightly by triggering on one MP-NAT–positive rather than two and increased substantially by increasing the duration from 7 to 14 days that no ID-NAT–positive donations are detected before resuming MP-NAT.

CONCLUSION: Most trigger strategies become effective when test results from at least 560 donations daily are considered. A 14-day ID-NAT period may improve safety relative to the increase in the number of tests performed.

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