West Nile virus infections projected from blood donor screening data, United States, 2003

Abstract

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.

Figure 1

Yield of West Nile virus nucleic acid amplification test (NAT) screening of 4,585,573 donations at American Red Cross and America's Blood Centers (constituting ≈95% of US collections) from July 1 to October 31, 2003. A total of 944 confirmed viremic donations were identified, including 770 that were detectable by minipool-NAT and 174 detectable only by individual donation NAT. MP, minipool; ID, individual donation.

Figure 2

Yield of minipool–nucleic acid testing of blood donors for West Nile virus RNA by state and month, 2003.

Figure 3

West Nile virus minipool–nucleic acid amplification testing (MP-NAT) yield and immunoglobulin M (IgM) and IgG seroprevalence estimates for North Dakota, during and ≈8 months after the 2003 epidemic period.

Figure 4

A) Projected number of West Nile virus (WNV) infections per 1,000 persons. B) Estimated total number of WNV infections per state during 2003 epidemic season.

Figure 5

Projected proportion of each state's population infected with West Nile virus versus the proportion of the state's population reporting neuroinvasive disease cases to the Centers for Disease Control and Prevention's ArboNET program. Data are excluded for 13 states: 6 states with neither minipool–nucleic acid amplification testing (MP-NAP) yield nor neuroinvasive cases, 6 states with 2 to 12 neuroinvasive cases but no MP-NAT yield, and 1 state with 1 MP-NAT–positive donor but no reported neuroinvasive cases.