Nucleic acid testing for west nile virus RNA in plasma enhances rapid diagnosis of acute infection in symptomatic patients

Although nucleic acid amplification testing ( NAAT) for West Nile virus ( WNV) is useful in screening blood donors, such methods have not been studied in symptomatic patients. For diagnosis of WNV infection, 1.0 mL of plasma was tested by NAAT, and WNV-specific immunoglobulin M was assayed. Of 276 WNV cases, 191 were tested by both serology and NAAT. Of these, 86 ( 45.0%), 111 ( 58.1%), and 180 ( 94.2%) were detected by NAAT, serology, and combined NAAT and serology, respectively. NAAT-based screening was most useful within 8 days of the onset of symptoms. Viremia is common in early symptomatic WNV infection, and NAAT enhances diagnostic yield.