Twenty-nine laboratory-confirmed West Nile virus (WNV) encephalitis patients were bled serially so that WNV-reactive immunoglobulin (Ig) M activity could be determined. Of those patients bled, 7 (60%) of 12 had anti-WNV IgM at approximately 500 days after onset. Clinicians should be cautious when interpreting serologic results from early season WNV IgM-positive patients.
Roehrig J, Nash D, Maldin B, Labowitz A, Martin DA, Lanciotti RS, Campbell GL. Persistence of Virus-Reactive Serum Imunoglobulin M Antibody in Confirmed West Nile Virus Encephalitis Cases. Emerg Infect Dis. 2003;9(3): 376-9. PMCID 2958550