Background: Diphtheria is uncommon in the World Health Organization (WHO) European Region. Nevertheless, sporadic cases, sometimes fatal, continue to be reported. Aim: To report on diphtheria cases and coverage with first and third doses of diphtheria, tetanus and pertussis vaccines (DTP1 and DTP3, respectively) for 2010–19 in the Region with a focus on 2019. Methods: Data on diphtheria cases were obtained from WHO/United Nations International Children's Emergency Fund (UNICEF) Joint Reporting Forms submitted annually by the Region’s Member States. WHO/UNICEF Estimates of National Immunization Coverage for DTP1 and DTP3 were summarised for 2010–19. For 2019, we analysed data on age, and vaccination status and present data by country on DTP1 and DTP3 coverage and the percentage of districts with ≥ 90% and < 80% DTP3 coverage. Results: For 2010–19, 451 diphtheria cases were reported in the Region. DTP1 and DTP3 coverage was 92–96% and 95–97%, respectively. For 2019, 52 cases were reported by 11 of 48 countries that submitted reports (including zero reporting). Thirty-nine countries submitted data on percentage of their districts with ≥ 90% and < 80% DTP3 coverage; 26 had ≥ 90% districts with ≥ 90% coverage while 11 had 1–40% districts with < 80% coverage. Conclusion: Long-standing high DTP3 coverage at Regional level probably explains the relatively few diphtheria cases reported in the Region. Suboptimal surveillance systems and inadequate laboratory diagnostic capacity may also be contributing factors. Still, the observed cases are of concern. Attaining high DTP3 coverage in all districts and implementing recommended booster doses are necessary to control diphtheria and prevent outbreaks.

Introduction. Diphtheria is a potentially life-threatening infection and remains endemic in many low- and middle-income countries (LMICs). A reliable, low-cost method for serosurveys in LMICs is warranted to estimate the accurate population immunity to control diphtheria. Hypothesis/Gap Statement. The correlation between the ELISA results against diphtheria toxoid and the gold standard diphtheria toxin neutralization test (TNT) values is poor when ELISA values are <0.1 IU ml⁻¹, which results in inaccurate estimates of susceptibility in populations when ELISA is used for measuring antibody levels. Aim. To explore methods to accurately predict population immunity and TNT-derived anti-toxin titres from ELISA anti-toxoid results. Methodology. A total of 96 paired serum and dried blood spot (DBS) samples collected in Vietnam were used for comparison of TNT and ELISA. The diagnostic accuracy of ELISA measurement with reference to TNT was assessed by area under the receiver operating characteristic (ROC) curve (AUC) and other parameters. Optimal ELISA cut-off values corresponding to TNT cut-off values of 0.01 and 0.1 IU ml⁻¹ were identified by ROC analysis. A method based on the multiple imputation approach was also applied to estimate TNT measurements in a dataset that only included ELISA results. These two approaches were then applied to ELISA results previously generated from 510 subjects in a serosurvey in Vietnam. Results. The ELISA results on DBS samples showed a good diagnostic performance compared to TNT. The cut-off values for ELISA measurement corresponding to the TNT cut-off values of 0.01 IU ml⁻¹ were 0.060 IU ml⁻¹ in serum samples, and 0.044 IU ml⁻¹ in DBS samples. When a cut-off value of 0.06 IU ml⁻¹ was applied to the 510 subject serosurvey data, 54 % of the population were considered susceptible (<0.01 IU ml⁻¹). The multiple imputation-based approach estimated that 35 % of the population were susceptible. These proportions were much larger than the susceptible proportion estimated by the original ELISA measurements. Conclusion. Testing a subset of sera by TNT combined with ROC analysis or a multiple imputation approach helps to adjust ELISA thresholds or values to assess population susceptibility more accurately. DBS is an effective low-cost alternative to serum for future serological studies for diphtheria.

Background: Streptococcus agalactiae (Group B Streptococcus, GBS) is a leading cause of neonatal sepsis in high-income countries. While intrapartum antibiotic screening reduces this risk, increasing resistance to macrolides and lincosamides in Europe since the 1990s has limited therapeutic options for penicillin-allergic patients. Reports of reduced beta-lactam susceptibility in GBS further emphasise the need for robust antimicrobial resistance (AMR) surveillance. However, broth microdilution (BMD) methods are unsuitable for large-scale antimicrobial susceptibility testing (AST). Objective: To demonstrate that agar-dilution AST provides equivalent results to broth dilution methods, with superior capacity for high-throughput screening. Methods: Agar-dilution and microdilution AST methods were compared using a panel of 24 characterised susceptible and resistant GBS strains for benzylpenicillin, chloramphenicol, clindamycin, erythromycin, gentamicin, levofloxacin, tetracycline, and vancomycin. Minimum inhibitory concentration (MIC) agreements were evaluated, and resistance profile correlations were assessed using Cohen’s kappa values. Results: Agar-dilution demonstrated >90% agreement with BMD MIC for most antimicrobials, except vancomycin (87.5%), erythromycin (83.33%), and tetracycline (52.78%). Cohen’s kappa values indicated strong agreement (0.88–1.00) for resistance determination. Agar-dilution avoided “trailing growth” issues associated with BMD and facilitated easier detection of non-GBS contaminants. Conclusions: Agar-dilution is a valid method for high-throughput AMR surveillance of retrospective cohorts (96 isolates per plate) and is critical for identifying emerging GBS resistance trends and informing therapeutic guidelines. However, due to the large number of plates required per antimicrobial, it is impractical for routine clinical diagnostics.