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


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.


CONCLUSIONS
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.
Biggerstaff
Brad J
BJ
Division of Vector-Borne Infectious Diseases, National Center for Zoonotic, Vector-Borne, and Enteric Diseases, Centers for Disease Control and Prevention, Fort Collins, CO 80521, USA. bbiggerstaff@cdc.gov
Petersen
Lyle R
LR
D000914:Antibodies, Viral / Q000097:blood; D001782:Blood Donors; D006801:Humans; D012367:RNA, Viral / Q000097:blood; D014902:West Nile virus / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*
D000914:Antibodies, Viral; D012367:RNA, Viral