Incidence and Transmission Dynamics of Bordetella pertussis Infection in Rural and Urban Communities, South Africa, 2016‒2018

Highlights of the 14th International Bordetella Symposium

Pertussis, or whooping cough, is a highly contagious and acute respiratory illness caused primarily by the gram-negative coccobacillus Bordetella pertussis. Despite near-universal vaccination, pertussis remains one of the least-controlled vaccine-preventable infectious diseases. Since 2023, pertussis incidence has been rising, and widespread pertussis outbreaks have resurged in many countries. In response to these emerging challenges, almost 300 experts from institutions across 24 countries convened at the 14th International Bordetella Symposium in Prague, Czech Republic, from 24 to 28 June 2024 to discuss pertussis epidemiology and research and strategies to mitigate the global pertussis burden. We present here the highlights of the symposium, comprising epidemiological and clinical aspects of Bordetella infections, results of clinical trials of pertussis vaccination in pregnant women and effectiveness of maternal vaccination in protecting newborn infants in Africa and Europe, the controlled human infection model (CHIM), and the latest insights into the biology, immunology, and pathogenesis of B. pertussis infection.

[Pertussis worldwide. Vaccinating children and adults]

Pertussis (whooping cough) is an important cause of morbidity and mortality in infants world-wide, and continues to be a public health concern despite high vaccination coverage. The disease, caused by bacterium Bordetella pertussis, is present in all countries. Before vaccines became widely available in the 1950s, pertussis was one of the most common childhood diseases worldwide. According to WHO, estimation of deaths was 4 millions/year in 1950 and 100 000/year in 2015. But morbidity remains important with a high circulation of the bacterium determining atypical clinical forms after whole cell or acellular vaccines use. This is due mainly to the absence of booster doses in adolescents and adults. Major progress are generalisation of PCR and vaccination of mother during pregnancy. A resurgence of pertussis is observed after generalisation of acellular vaccines use. In China the progression of allele ptxPl was found in all areas following the use of acellular vaccine. This allele, rare before acellullar vaccine, is linked to a macrolide resistance, and reaches more than 30% of strains isolated in hospitalised children.These evolutions must be evaluated in clinical forms and genotyping of all strains, in all areas.

Genomic characterization of Bordetella pertussis in South Africa, 2015-2019

Pertussis remains a public health concern in South Africa, with an increase in reported cases and outbreaks in recent years. Whole genome sequencing was performed on 32 Bordetella pertussis isolates sourced from three different surveillance programmes in South Africa between 2015 and 2019. Genome sequences were characterized using multilocus sequence typing, vaccine antigen genes (ptxP, ptxA, ptxB, prn and fimH) and overall genome structure. All isolates were sequence type 2 and harboured the pertussis toxin promoter allele ptxP3. The dominant genotype was ptxP3-ptxA1-ptxB2-prn2-fimH2 (31/32, 96.9 %), with no pertactin-deficient or other mutations in vaccine antigen genes identified. Amongst 21 isolates yielding closed genome assemblies, eight distinct genome structures were detected, with 61.9 % (13/21) of the isolates exhibiting three predominant structures. Increases in case numbers are probably not due to evolutionary changes in the genome but possibly due to other factors such as the cyclical nature of B. pertussis disease, waning immunity due to the use of acellular vaccines and/or population immunity gaps.

Assessing the Underestimation of Adult Pertussis Disease in Five Latin American Countries

INTRODUCTION

Pertussis, a contagious respiratory disease, is underreported in adults. The study objective was to quantify underestimation of pertussis cases in adults aged ≥ 50 years in five Latin American countries (Argentina, Brazil, Chile, Mexico, Peru).

METHODS

A previously published probabilistic model was adapted to adjust the number of pertussis cases reported to national surveillance systems by successive multiplication steps (proportion of pertussis cases seeking healthcare; proportion with a specimen collected; proportion sent for confirmatory testing; proportion positive for pertussis; proportion reported to passive surveillance). The proportions at each step were added in a random effects model to produce a pooled overall proportion, and a final multiplier was calculated as the simple inverse of this proportion. This multiplier was applied to the number of cases reported to surveillance to estimate the number of pertussis cases. Monte Carlo simulation with 10,000 iterations estimated median as well as upper and lower 90% values. Input data were obtained from surveillance systems and published sources.

RESULTS

The estimated median underestimation factor for pertussis cases in adults ranged from 104 (90% limits 40, 451) in Chile to 114 (90% limits 39, 419) in Argentina. In all five countries, the largest estimated number of cases was in the group aged 50-59 years. The highest number per 100,000 population was in the group aged ≥ 90 years in most countries. The estimated median underestimation factor for pertussis hospitalizations was 2.3 (90% limits 1.8, 3.3) in Brazil and 2.4 (90% limits 1.8, 3.2) in Chile (data not available for other countries).

CONCLUSION

This analysis indicates that the number of pertussis cases in adults aged ≥ 50 years in five Latin American countries is approximately 100 times higher than the number captured in surveillance data. These results could support decision-making in the diagnosis, management, and prevention of pertussis disease in adults.