Streptococcus pneumoniae remains a significant cause of respiratory infections and invasive diseases worldwide. While pneumococcal conjugate vaccines (PCVs) have dramatically reduced the incidence of invasive disease caused by vaccine-covered serotypes, non-vaccine types (NVTs) have emerged in their place. A retrospective analysis by researchers at the Laboratory of Medical Microbiology (LMM) at the University of Antwerp sheds light on the increasing prevalence of serotype 23B in Belgium, particularly the newly identified 23B1 genotype, which is driving antibiotic resistance and invasive disease among children.
Tracking the emergence of 23B1
The study analyzed pneumococcal carriage in children attending Belgian daycare centers and pediatric invasive pneumococcal disease (IPD) cases over several years. Whole-genome sequencing of 716 isolates revealed that 23B1, a genetic variant of the 23B serotype, has been increasing in prevalence since 2013. Notably, the peak in 23B1 carriage in 2020-2021 coincided with a rise in IPD cases caused by this genotype.
One of the most concerning findings is the high level of penicillin non-susceptibility associated with 23B1. While 23B0, the original genotype, is associated with penicillin susceptibility, 23B1 isolates demonstrated significantly higher minimum inhibitory concentrations (MICs) for penicillin. This suggests that 23B1 might play a key role in reducing the effectiveness of standard antibiotic treatments.
The role of vaccination and COVID-19 in 23B1’s expansion
Belgium has undergone multiple shifts in pneumococcal vaccination strategies over the years, alternating between PCV7, PCV13, and PCV10. The study suggests that changes in vaccine coverage may have inadvertently allowed non-vaccine serotypes like 23B1 to expand. Additionally, the COVID-19 pandemic may have played a role in these shifts. Public health measures during the pandemic, including reduced social interactions and mask mandates, influenced bacterial transmission dynamics, potentially altering pneumococcal carriage patterns.
Global relevance and public health implications
The rise of 23B1 is not unique to Belgium. Similar trends have been reported in the UK, USA, and other European countries, highlighting the need for continuous global surveillance of pneumococcal serotypes. The findings from this study emphasize the importance of monitoring pneumococcal carriage in daycare centers, as changes in the bacterial landscape among healthy children often foreshadow shifts in invasive disease trends.
This research underscores the necessity of adapting vaccination policies to address emerging non-vaccine serotypes. Future vaccine formulations, such as the 21-valent PCV, may provide broader protection. In the meantime, maintaining high levels of pneumococcal surveillance and antibiotic stewardship will be critical in managing the spread of resistant strains like 23B1.
For more details, access the full study published in the Journal of Clinical Microbiology here.