Persistence of West Nile Virus Immunoglobulin M Antibodies, Greece

A major outbreak of West Nile virus (WNV) lineage 2 infections was observed in 2010 in Greece. In order to check the persistence of WNV IgM antibodies, a second serum sample taken 75-180 days after onset of the illness from 29 patients with WNV infection was tested. A third sample was obtained 181-270 days after onset of the illness from 8 of the 12 patients with IgM-positive second sample. Mixed effects linear regression analysis indicated that the approximate time at which IgM index became negative was 164 (95% confidence interval, 95% Cl 99-236) days after the symptoms' onset. Persistence of IgM antibodies was observed in 12% of patients at 181-270 days of follow-up. A sharp decrease in the IgM levels was observed, mainly in patients who had high IgM index value in the acute phase. All patients were WNV IgG positive at the follow-up. J. Med. Virol. 83:1857-1860, 2011. (C) 2011 Wiley-Liss, Inc.