Performance of four IgM antibody assays in the diagnosis of Measles virus primary infection and cases with a serological profile indicating reinfection.

Objectives: To determine the diagnostic performance of four commercially available IgM tests in the diagnosis of measles virus (MeV) primary infection and cases with a serological profile indicating reinfection.Methods: Sera from 187 patients with MeV primary infection, 30 patients with suspected reinfection (after vaccine failure) and 153 patients with rash-like symptoms after exclusion of MeV infection were retested with four IgM tests. MeV infection was verified by RT-PCR, primary and suspected reinfections were differentiated by IgG avidity and neutralization assays.Results: All IgM assays displayed significant agreement (Cohen's κ≥0.604, all p<0.001) and a higher diagnostic accuracy in primary infection than in suspected reinfection (indicated by high IgG avidity and significantly higher Anti-MeV-IgG and neutralizing titers). In the overall cohort, the area under the curves (AUC) were comparable among all tests, ranging from 0.875 to 0.931, with ranges increasing to 0.911-0.930 in the primary infection and decreasing to 0.765-0.940 in the setting of high Anti-MeV-IgG avidity, and all tests displayed high specificity (81.1-92.2%). Of note, IgM tests with the highest diagnostic accuracy had discriminatory abilities not significantly different than PCR from serum.Conclusions: Although reinfections pose a challenge for IgM testing, IgM assays remain a cornerstone in the diagnosis of MeV infections. Especially in samples with a serological profile indicating reinfections, IgM tests displayed an equal or even superior diagnostic ability as compared to PCR from serum.