Direct and indirect effects of 13-valent pneumococcal conjugate vaccine on pneumococcal carriage in children hospitalised with pneumonia from formal and informal settlements in Mongolia: an observational study

Streptococcus pneumoniae serotype 33H: a novel serotype with frameshift mutations in the acetyltransferase gene wciG

BACKGROUND

Streptococcus pneumoniae (the pneumococcus) is a leading cause of community-acquired pneumonia. Pneumococci are categorised into serotypes, based on the type of capsular polysaccharide produced, which has important implications for virulence, vaccine impact and global surveillance. Recently, we identified a novel serotype, which we named 33G, that is comprised of an O-acetylated hexasaccharide repeat unit. In this study, we report and describe variants of 33G, designated 33G-like, which we isolated from the nasopharynx of two adults hospitalised with pneumonia in Mongolia.

METHODS

Serological comparison of 33G and 33G-like pneumococci were conducted by Quellung serotyping. Genetic analysis of the capsular polysaccharide loci was performed using whole genome sequencing. Polysaccharide composition was determined using 1H nuclear magnetic resonance.

RESULTS

By Quellung serotyping, 33G pneumococci type as both 10B and 33B whereas 33G-like pneumococci type as both 10B and 33F. Genomic analysis of the capsular polysaccharide locus revealed 33G-like loci are identical to 33G, except for frameshift mutations in the wciG gene which encodes an acetyltransferase responsible for the O-acetylation of beta-galactofuranose (β-Galf) in the capsular polysaccharide repeat unit. We constructed an artificial 33G-like by deleting wciG in a 33G strain and confirmed this gene was responsible for the serological differences between 33G and 33G-like pneumococci. Lastly, 1H nuclear magnetic resonance confirmed the O-acetylation present in the 33G polysaccharide is absent in the 33G-like polysaccharide.

CONCLUSIONS

Here, we have provided serological, genetic and biochemical evidence that the 33G-like capsule differs to 33G and all other pneumococcal serotypes, meeting the requirements to be designated as a new serotype, which we have named 33H.

Microbiological aetiology of paediatric respiratory tract infections in Kyrgyzstan

INTRODUCTION

Respiratory tract infections (RTIs) are a leading cause of morbidity and mortality in children worldwide. Aetiologic virus and bacteria vary geographically. To date, no systematic data on RTI aetiologies have been published from Kyrgyzstan, a country with a high under-five mortality from lower RTIs and a widespread overuse of antibiotics. We aimed to identify the aetiologies of RTI in children in Kyrgyzstan and to assess the pneumococcal conjugate vaccine (PCV) vaccination rate and the correlation with the detection of Streptococcus pneumoniae in our population.

METHODS

We collected samples from children aged 6 months to 12 years presenting with symptoms of acute RTI for outpatients or diagnosed with pneumonia for inpatients. Samples were collected from November 2022 to June 2023 and were analysed using standard culture methods and real-time polymerase chain reaction (RT-PCR) to identify bacterial, viral, and atypical bacterial pathogens. We obtained the vaccination status through vaccination records and parents' recollections.

RESULTS

Positive bacteriologic cultures were found for 294 (25.0%) of 1174 outpatients and 83 (27.7%) of 300 inpatients. S. pneumoniae was the most commonly found bacterial pathogen in both groups, making up 44.8% of all cultured bacteria. Furthermore, 445 (64.1%) of 694 outpatients with RT-PCR performed had one or more viral pathogens identified, while this was the case for 162 (54.7%) of 296 inpatients. Mycoplasma pneumoniae was identified in 15.8% of inpatients possibly representing an epidemic in the spring of 2023. Approximately 20% of both in- and outpatients had a viral-bacterial simultaneous detection. 87.1% of outpatients and 75.9% of inpatients had been vaccinated with PCV. We found a higher proportion of unvaccinated children among those under five years of age and a higher carriage rate of S. pneumoniae among unvaccinated inpatients.

CONCLUSION

In this study, we found a high prevalence of viral infections and viral-bacterial simultaneous detections among Kyrgyz children with respiratory tract infections (RTI). The findings from this study can inform new clinical guidelines for local health workers and lead to more targeted use of antibiotics and improved health outcomes for children in Kyrgyzstan.

CLINICAL TRIAL

Not applicable.

Effect of Pneumococcal Conjugate Vaccine on Pneumonia Incidence Rates among Children 2-59 Months of Age, Mongolia, 2015-2021

Starting in June 2016, the 13-valent pneumococcal conjugate vaccine (PCV13) was introduced into the routine immunization program of Mongolia by using a 2+1 dosing schedule, phased by district. We used prospective hospital surveillance to evaluate the vaccine's effect on pneumonia incidence rates among children 2-59 months of age over a 6-year period. Of 17,607 children with pneumonia, overall adjusted incidence rate ratios showed decreased primary endpoint pneumonia, very severe pneumonia, and probable pneumococcal pneumonia until June 2021. Results excluding and including the COVID-19 pandemic period were similar. Pneumonia declined in 3 districts that introduced PCV13 with catch-up campaigns but not in the 1 district that did not. After PCV13 introduction, vaccine-type pneumococcal carriage prevalence decreased by 44% and nonvaccine-type carriage increased by 49%. After PCV13 introduction in Mongolia, the incidence of more specific pneumonia endpoints declined in children 2-59 months of age; additional benefits were conferred by catch-up campaigns.

Streptococcus pneumoniae serotype 33G: genetic, serological, and structural analysis of a new capsule type

IMPORTANCE

Streptococcus pneumoniae (the pneumococcus) is a bacterial pathogen with the greatest burden of disease in Asia and Africa. The pneumococcal capsular polysaccharide has biological relevance as a major virulence factor as well as public health importance as it is the target for currently licensed vaccines. These vaccines have limited valency, covering up to 23 of the >100 known capsular types (serotypes) with higher valency vaccines in development. Here, we have characterized a new pneumococcal serotype, which we have named 33G. We detected serotype 33G in nasopharyngeal swabs (n = 20) from children and adults hospitalized with pneumonia, as well as healthy children in Mongolia. We show that the genetic, serological, and biochemical properties of 33G differ from existing serotypes, satisfying the criteria to be designated as a new serotype. Future studies should focus on the geographical distribution of 33G and any changes in prevalence following vaccine introduction.