Evaluation of 15 commercial enzyme immunoassays for the detection of rubella-specific IgM

Background: Detection of rubella-specific IgM is a critical investigation in the diagnosis of recent or congenital rubella for which many commercial enzyme immunoassays (EIAs) are now available. Objectives: To evaluate 15 commercially-available EIA kits for the detection of rubella-specific IgM. Study design: A panel of 229 sera was established comprising 72 sera from cases of primary rubella, re-infection, congenital rubella and primary immunization in which rubella-specific IgM had been detected by M-antibody capture radioimmunoassay (MACRIA); 80 sera, negative by MACRIA and no evidence of recent illness; 77 sera from recent illness with a number of other microbial agents, sera containing rheumatoid factor, and sera previously shown to give non-specific reactivity by MACRIA. These sera were tested in 15 commercial EIA kits for rubella-specific IgM according to the manufacturers' instructions. Sensitivity and specificity for each assay was established. Results: Specificities ranged from 82-98%, improving to 88-100% if the previously established non-specific reactive sera were excluded. Sensitivities ranged from 63-92%. Although only two sera from congenital rubella were tested, for one serum only four assays detected specific IgM. Conclusion: Some commercial EIAs for rubella-specific IgM now give an acceptable balance of sensitivity and specificity, but all assays may give reactivity with occasional sera where there is no supporting evidence for recent primary rubella or rubella reinfection.