West Nile fever characteristics among viremic persons identified through blood donor screening

Abstract

Nucleic acid testing (NAT) of blood donors provides opportunities for identifying West Nile virus (WNV)-infected persons before symptoms develop and for characterizing subsequent illness. From June 2003 through 2008, the American Red Cross performed follow-up interviews with and additional laboratory testing for 1436 donors whose donations had initial test results that were reactive for WNV RNA; 821 of the donors were subsequently confirmed to have WNV infection, and the remainder were unconfirmed or determined to have false-positive results. Symptoms attributed to WNV infection were determined by comparing symptom frequency among 576 donors identified with early WNV infection (immunoglobulin M antibody negative) and those with unconfirmed infection. We estimate that 26% of WNV-infected persons become symptomatic, defined by the presence of at least 3 of 8 indicator symptoms. Nearly one-half of symptomatic persons sought medical care; only 5% received a diagnosis of WNV infection. Female subjects and persons with higher viral loads detected in the index donation were more likely than other subjects to develop symptoms. © 2010 by the Infectious Diseases Society of America. All rights reserved.