National blood donor screening for West Nile virus (WNV)
RNA using minipool
nucleic acid amplification testing (MP-
NAT) was implemented in the United States in July 2003. We compiled national
NAT yield data and performed WNV
immunoglobulin M (
IgM) testing in 1 WNV-epidemic region (North Dakota). State-specific MP-
NAT yield, antibody seroprevalence, and the average time
RNA is detectable by MP-
NAT were used to estimate incident
infections in 2003. WNV
donor screening yielded 944 confirmed viremic donors. MP-
NAT yield peaked in August with >0.5% of donations positive for WNV
RNA in 4 states. Peak
IgM seroprevalence for North Dakota was 5.2% in late September. The average time
viremia is detectable by MP-
NAT was 6.9 days (95% confidence interval [CI] 3.0-10.7). An estimated 735,000 (95% CI 322,000-1,147,000)
infections occurred in 2003, with 256 (95% CI 112-401)
infections per neuroinvasive case. In addition to preventing transfusion-transmitted
WNV infection,
donor screening can serve as a tool to monitor seasonal incidence in the general population.