FIG. 5.

Summary of the proportions of immunized subjects with titers of ≥1:4 in SBA, OPA, or PP assays. The bars represent the proportions of preimmunization (open bars) or postimmunization (filled bars) sera that were positive when tested at a 1:4 dilution in each assay. Error bars, 95% confidence intervals (CI). A positive serum SBA or OPA titer was defined as a 50% decrease, after a 60-min incubation of bacteria, from the CFU/ml at time zero. Positive PP activity was defined as a ≥0.5 log₁₀ decrease, after a 90-min incubation, from the CFU/ml at time zero. Depending on the strain, postimmunization PP activity was 2.6- to 2.8-fold more frequent then an SBA titer of ≥1:4.