Performance Characteristics of Six Immunoglobulin M (IgM) ELISA Assays Used for Laboratory Confirmation of Measles

Laboratory confirmation of infection is an essential component of measles surveillance. Detection of measles specific IgM in serum by enzyme linked immunosorbent assay (ELISA) is the most used method for confirming measles infection. ELISA formats vary as does the sensitivity and specificity of each assay. Specimens collected within 3 days of rash onset can yield a false negative result, which can delay confirmation of measles cases. Interfering substances can yield a false positive result, leading to unnecessary public health interventions. The IgM capture assay developed at the Centers for Disease Control (CDC) was compared against 5 commercially available ELISA kits for the ability to detect measles virus-specific IgM in a panel of 90 well-characterized specimens. Serum samples were tested in triplicate using each commercial kit as recommended by the manufacturer. Using the CDC measles IgM capture assay as the reference test; sensitivity and specificity for the commercial kits ranged from 50 to 83% and 86.9 to 98%, respectively. Discrepant results were observed for samples tested with all five commercial kits and ranged from 13.8 to 28.8% of the specimens tested. False positive results occurred in 2.0 to 13.1% of sera while negative results were observed in 16.7 to 50% of sera that were positive by the CDC measles IgM capture assay. Evaluation and interpretation of measles IgM serologic results can be complex, particularly in measles elimination settings. The performance characteristics of a measles IgM assay should be carefully considered when selecting an assay to achieve high quality measles surveillance.