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% CI 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. © 2011 Wiley‐Liss, Inc.