[Diagnostic value of serum IgM determination in human infections caused by Flaviviruses].

Since 1977, we have performed arboviruses' serosurveys in 330 patients by haemagglutination inhibition test. For 22 of them we have studied specific IgM antibodies against flavivirus. The separation was done by sucrose-gradient density ultracentrifugation and IgM antibodies were demonstrated by the HI test. The 22 IgM tested sera were distributed as follows: 1) 7 positive sera corresponding to patients with a recent flavivirus infection; 2) 12 sera to test with a HI titer greater than or equal to 20 against one or more flaviviruses on a single serum; and 3) 3 negative control sera corresponding to patients with a past known flavivirus infection. For the first group of sera, IgM assay was used to help to determine the causal virus and for the sera to test, it led to conclude to a recent infection in one case and to a past infection in eleven others.