Fig. 2. Percentage of pertussis infected sera in the two age groups (40–49 and 50–59) separately and in the total cohort, and subdivided by sex per country (Y-axis).

On the X-axis the percentage of seroprevalence for PT ≥ 100 IU/mL is displayed. The dots indicate the estimated seroprevalence, the bars the corresponding 95% confidence intervals. The estimates and p values of the differences are obtained by a binomial generalised linear regression model, in which a modified logit link function is used to correct for a specificity of 0.98 and a sensitivity of 0.78. Abbreviations of all participating countries and the number of samples included in the study are listed in Table 1.