West Nile viremic blood donors and risk factors for subsequent West Nile fever.

Background: While increasing age is a known risk factor for neuroinvasive West Nile virus (WNV) disease, little is known about risk factors for West Nile fever (WNF). In 2003, United States blood centers identified WN (West Nile) viremic donors using nucleic acid-amplification tests (NATs), making it possible to prospectively determine risk factors for WNF. We report the characteristics of WN viremia among donors at Colorado's largest blood center and risk factors for WNF in viremic donors.