Development of a highly specific and sensitive rubella immunoglobulin M antibody capture enzyme immunoassay that uses enzyme-labeled antigen.

An enzyme immunoassay (EIA) for serum immunoglobulin M (IgM) antibodies to rubella virus based on enzyme labeling of viral antigen was developed. The sensitivity of the EIA for the detection of recent rubella virus infection was evaluated by using 115 rubella-IgM-antibody-positive serum specimens, which were confirmed as positive by Rubazyme M (Abbott Diagnostics). In addition, 12 individuals, 2 of whom were exposed to rubella through vaccination and 10 of whom were exposed through natural infection, were studied, and the results were compared with those obtained by indirect EIA (Rubelisa M; Electro-Nucleonics, Inc.) and immunoblotting. The sensitivity of the newly developed EIA with sera from these individuals was 100%. Serum specimens from two patients indicated that the IgM antibodies were detected by the newly developed EIA at the same time as IgM antibodies were detected by immunoblotting and before positive reactions were detected by an indirect EIA. The reference population consisted of 564 healthy blood donors and hospitalized patients (150 serum specimens). In addition, 145 serum specimens commonly giving false-positive reactions in conventional rubella IgM EIAs were studied. With these specimens, no false-positive reactions were observed. Positive IgM responses, which could not be confirmed by immunoblotting, were observed in two samples from the reference population. However, these two samples were rubella IgG positive. The overall specificity of the EIA was 99.8%.