Estimated risk of West Nile virus transmission through blood transfusion during an epidemic in Queens, New York City.
BACKGROUND
Human West Nile virus (WNV) infection has been documented in the eastern United States since its discovery there in 1999. Epidemics of WNV encephalitis and meningitis raise concern that transmission of WNV may occur through voluntary blood donations.


METHODS
Case onset dates from the 1999 Queens, NY, epidemic of WNV encephalitis and meningitis, and historic data on viremia in humans are used to estimate the number of cases that were viremic throughout the epidemic. Estimates of the inapparent-to-apparent WNV infection ratio, the proportion of asymptomatic infections reported in a seroepidemiologic survey coincident with the epidemic, and the population size are used to infer the WNV transfusion-transmission risk. Statistical resampling methods are used.


RESULTS
The maximum and mean risk of WNV transmission (/10,000) from donors in Queens were estimated as 2.7 (95% CI, 0.9-5.6) and 1.8 (95% CI, 1.4-2.2), respectively. The risk peaked in late August, with very low risk before August and after September.


CONCLUSIONS
Although most WNV-infected individuals have subclinical infections, these data suggest a low prevalence of viremia throughout the Queens epidemic and subsequent low risk of transmission of WNV by blood transfusion.
Biggerstaff
Brad J
BJ
Division of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, CDC, Fort Collins, CO 80522-2087, USA. bbiggerstaff@cdc.gov
Petersen
Lyle R
LR
D001782:Blood Donors; D004196:Disease Outbreaks; D006801:Humans; D009519:New York City / Q000453:epidemiology; D018570:Risk Assessment; D065227:Transfusion Reaction; D014766:Viremia / Q000453:epidemiology; D014901:West Nile Fever / Q000453:epidemiology* / Q000635:transmission*