Comparison of Coccidioides Antibody Detection by the MVista Enzyme Immunoassay with Immunodiffusion and Complement Fixation

Background: Enzyme immunoassays have several advantages over classic serological techniques, including improved sensitivity. There are currently two commercial Coccidioides antibody detection EIAs available with high specificities but lower sensitivities, 68% and 72% (Sunenshine, R ICAAC 2014). The purpose of this study is to evaluate an EIA method for measurement of anti-CoccidioidesIgM and IgG antibodies in an assay developed at MiraVista® Diagnostics.

Methods: A total of 100 serum samples that were submitted for anti-Coccidioides antibody testing by immunodiffusion (ID) and complement fixation (CF) to the Kern County Public Health service laboratory. Specimens were concentrated 8-fold before ID testing and reported as positive, weakly positive, very weakly positive or negative. The clinical diagnosis of these individuals was unknown, but 51 of the specimens were positive for Coccidioidesantibody by ID and/or CF.

For EIA analysis specimens were diluted and added to wells of antigen coated microplate and incubated for one hour. Antibody is detected using biotinylated anti-human IgM or IgG conjugates. Results are expressed as units determined by extrapolation from a standard curve. Results of ≥10 units were classified as positive, 8.0-9.9 units as indeterminate, and 0 to 7.9 units as negative.

Results: IgG antibodies were detected by EIA in 31/36 (86.1%) specimens tested positive for antibody by CF. IgG antibodies were also detected in 8/64 (12.5%) specimens that were negative by CF. IgG antibodies were detected by EIA in 32/45 (71.1% %) specimens that were positive for antibody by IDCF. Negative results occurred in 13 (28.9%) specimens that were weakly (3) or very weakly (10) positive by IDCF, four of which had indeterminate results by EIA. IgG antibodies were detected in 7/55 (12.7%) specimens that were negative by IDCF. IgM antibodies were detected in 18/28 (64.3%) of specimens that were positive by IDTP. IgM negative specimens were weakly or very weakly positive by IDTP. IgM antibodies were detected by EIA in 6/72 (8.3%) specimens that were negative by IDTP.

Conclusion: : IgG and IgM antibody detection by EIA demonstrated good agreement with ID and CF. Disagreement occurred in specimens that were weakly positive by ID, CF or EIA. Additional studies are required to determine sensitivity and specificity in known cases and controls.