FIG. 4.

Accuracy or selectivity of the IsdB serologic assay. A. IsdB antibody concentration for the IsdB human reference serum from vaccinees was added to five IsdB antibody low-concentration sera to evaluate the percent recovery in the assay. The reference standard was added into low anti-IsdB concentration sera at concentration levels of 5, 40, 100, 200, and 320 μg/ml. Background antibody levels were subtracted from the measured levels. Error bars represent 2 standard deviations from the means. B. Percent recovery in the IsdB serologic assay. The percent recovery in the IsdB serologic assay was determined by subtracting the IsdB-specific background antibody levels from the measured values and determining the percent recovery of observed over expected values. White bars represent samples tested at a 1:2,500 dilution and black bars represent samples tested at a 1:25,000 dilution.