Performance of Four IgM Antibody Assays in the Diagnosis of Measles Virus Primary Infection and Cases with a Serological Profile Indicating Reinfection.

The object of this study was 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. 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 reverse transcriptase PCR (RT-PCR), and primary and suspected reinfections were differentiated by IgG avidity and neutralization assays. All IgM assays displayed significant agreement (Cohen's κ, ≥0.604; all  < 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 areas under the curve (AUC) were comparable among all tests, ranging from 0.875 to 0.931, with ranges increasing to 0.911 to 0.930 in the primary infection and decreasing to 0.765 to 0.940 in the setting of high anti-MeV-IgG avidity, and all tests displayed high specificity (81.1 to 92.2%). Of note, IgM tests with the highest diagnostic accuracy had discriminatory abilities not significantly different than PCR from serum. 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 compared to PCR from serum.