Comparison of mumps-IgM ELISAs in acute infection.

BACKGROUND: In Scotland there has been an outbreak of mumps with over 4000 confirmed cases in the last 2 years. As laboratory diagnosis is usually requested on patients with symptoms, a prompt diagnosis early in the illness is required. OBJECTIVES: To assess the performance of the five different commercial IgM-ELISAs used in Scottish Virus laboratories. STUDY DESIGN: The Specialist Virology Laboratory (SVC) Edinburgh distributed a serum panel to all Scottish laboratories that diagnose mumps by IgM-ELISA. The panel consisted of 45 sera from patients with confirmed mumps (date of onset known for 44/45) and 11 sera from patients with alternative diagnoses. Each laboratory performed their own commercial IgM-ELISAs blindly and reported results to the SVC Edinburgh. RESULTS: Sensitivity ranged from 24% to 51%. Assays performed better on samples taken later than 10 days after onset of symptoms. Specificity was about 82% for most assays. CONCLUSION: The sensitivity of commercial mumps IgM-ELISAs varied greatly. The Microimmune mumps-IgM ELISA had the best overall sensitivity in acute serum specimens. Diagnostic laboratories should be developing the means to perform direct detection of mumps virus for acute presentation and requesting convalescent bloods, if acute blood samples have no detectable IgM.