Circulation of pertussis and poor protection against diphtheria among middle-aged adults in 18 European countries

Abstract

Reported incidence of pertussis in the European Union (EU) and the European Economic Area (EEA) varies and may not reflect the real situation, while vaccine-induced protection against diphtheria and tetanus seems sufficient. We aimed to determine the seroprevalence of DTP antibodies in EU/EEA countries within the age groups of 40-49 and 50-59 years. Eighteen countries collected around 500 samples between 2015 and 2018 (N = 10,302) which were analysed for IgG-DTP specific antibodies. The proportion of sera with pertussis toxin antibody levels ≥100 IU/mL, indicative of recent exposure to pertussis was comparable for 13/18 countries, ranging between 2.7-5.8%. For diphtheria the proportion of sera lacking the protective level (<0.1 IU/mL) varied between 22.8-82.0%. For tetanus the protection was sufficient. Here, we report that the seroprevalence of pertussis in these age groups indicates circulation of B. pertussis across EU/EEA while the lack of vaccine-induced seroprotection against diphtheria is of concern and deserves further attention.

Fig. 1. Relative distribution of samples by IgG intervals and by country.

IgG-PT (a), IgG-Dt (b) and IgG-TT (c). Proportion of pertussis seroprevalence divided in samples <0.85 IU/mL (yellow), 0.85 to <50 IU/mL (green), 50 to <100 IU/mL (blue) and ≥100 IU/mL (purple) and seroprotection against diphtheria and tetanus in <0.01 IU/mL (purple), 0.01 to <0.1 IU/mL (green) and ≥0.1 IU/mL (yellow) within the 18 countries. The bars sum up to 100%. Abbreviations of all participating countries and the number of samples included in the study are listed in Table 1.

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.

Fig. 3. Percentage of sera protected against diphtheria 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 lack of seroprotection against diphtheria for IgG-Dt <0.01 IU/mL (a) and <0.1 IU/mL (b) 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 with logit link function. Abbreviations of all participating countries and the number of samples included in the study are listed in Table 1.

Fig. 4. Percentage of sera protected against tetanus 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 lack of seroprotection against tetanus for IgG-TT < 0.01 IU/mL (a) and <0.1 IU/mL (b) 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 using exact binomial methods. Abbreviations of all participating countries and the number of samples included in the study are listed in Table 1.

Fig. 5. Reverse cumulative distribution curves for IgG-PT (IU/mL) illustrated by increasing values at 50% per country.

Values below the LLOQ are not included. Abbreviations of all participating countries and the number of samples included in the study are listed in Table 1.