Detection of antibodies to Coccidioides immitis by enzyme immunoassay

Two hundred twenty-six specimens (160 serum samples, 66 cerebrospinal fluid samples) were tested with the Meridian Premier Coccidioides enzyme immunoassay (MPC-EIA), and the results were compared with those of conventional serologic tests detecting complement-fixing (CF) and tube precipitin (TP) antibodies. Of the 73 positive specimens by CF, 72 were positive by MPC-EIA (72 IgG positive, 48 IgM positive) and 1 was indeterminate. Of the 132 specimens negative by CF, 126 were negative by MPC-EIA, 3 were IgM positive only, and 3 were indeterminate. Of the three patients with specimens positive for IgM only, CF demonstrated seroconversion within a month in one. All 21 specimens that displayed anticomplementary activity by CF were confirmed negative by agar gel immunodiffusion for CF antibodies (IDCF) and TP antibodies (IDTP); 20 of these serum samples were also negative by MPC-EIA, and 1 was indeterminate. After exclusion of the 25 specimens with anticomplementary or indeterminate activity, results of MPC-EIA were in agreement with those of CF in 99% of specimens. With CF as reference, MPC-EIA had a specificity of 98%, sensitivity of 100%, and positive and negative predictive values of 96% and 100%, respectively. Correlation coefficient values from linear regressions of log-2 CF titer vs MPC-EIA IgG index values were calculated at .290 for serum samples and .931 for cerebrospinal fluid.