Fig. 4

The prevalence of anti-Bordetella pertussis toxin antibody and geometric mean titers (GMTs) in the study population. The x-axis represents the five age groups and the sample size in each age group. The scale on the right represents the proportion (%) of the population with positive anti-Bordetella pertussis toxin antibody. The scale on the left represents the GMTs in each age group, with the means indicated as a red line. Antibody measurements were negative (white), 5 to < 40 IU/ml (light blue), 40 to < 100 IU/ml (blue), and >100 IU/ml (dark blue)