Increase in prevalence of Streptococcus pneumoniae serogroup 24 in children upon introducing 13-valent pneumococcal conjugate vaccine in Japan

Rebound of pediatric invasive pneumococcal disease in Portugal after the COVID-19 pandemic was not associated with significant serotype changes

OBJECTIVES

The COVID-19 pandemic led to the institution of public health measures in many countries which reduced respiratory infections. We aimed to identify and characterize changes in pediatric (<18 years) invasive pneumococcal disease (pIPD) in Portugal in 2018-2023.

METHODS

pIPD cases were identified by culture and molecular methods and stratified by age and serotype. When available the susceptibility of the isolates to antimicrobials was evaluated.

RESULTS

pIPD cases were markedly reduced in the last trimester of 2019-2020 and the entire 2020-2021 season. While 2021-2022 was in line with pre-pandemic seasons, in 2022-2023, the number of pIPD cases exceeded those found pre-pandemic. Molecular tests were responsible for identifying and serotyping 30% of cases, highlighting their importance in evaluating pIPD. Among the 316 pIPD cases, 37 different serotypes were detected, of which serotypes 3 (n = 85, 26.9%), 8 (n = 25, 7.9%), 10A (n = 21, 6.6%) and 24F (n = 20, 6.3%) were the most frequent. The post-pandemic serotype distribution reflected mostly pre-pandemic trends and the rebound was not driven by particular serotypes. We identified many vaccine failures, most (n = 37) representing serotype 3 infections. Penicillin non-susceptibility increased from 14% pre-pandemic to 29%, with serotype 24F becoming particularly significant.

CONCLUSIONS

The higher number of cases of pIPD post-COVID-19 in Portugal raises the possibility of a higher burden of pneumococcal disease in Europe post-pandemic. The relatively stable serotype distribution and the current availability of the higher valency conjugate vaccines PCV15 and PCV20, potentially preventing a large proportion of pIPD (43% and 67%, respectively), offer an opportunity to control this increase.

Genetic characteristics of invasive pneumococcal disease-derived Streptococcus pneumoniae of serogroup 24 isolated in Tokyo, Japan

BACKGROUND

Since the introduction of the national routine vaccination program against Streptococcus pneumoniae in Japan from the early 2010s, the incidence of invasive pneumococcal disease (IPD) caused by non-vaccine serotypes has increased. This study focused on non-vaccine serogroup 24 strains derived from IPD and aimed to clarify their genetic characteristics.

METHODS

Between 2013 and 2022, 121 strains identified as serogroup 24 in patients with IPD were collected and applied to multilocus sequence typing and next-generation sequencing. Whole-genome data were used to delineate phylogenetic relationships and to identify virulence and antimicrobial resistance-associated genes.

RESULTS

Recent trends in sequence types (STs) were characterized by an increase in the proportion of ST162 and ST2754 for 24F and 24B, respectively, after 2018. Whole-genome phylogenetic analysis demonstrated that serogroup 24 strains were organized into three clades, closely related to STs but not with serotypes. All ST162 strains were classified as Global Pneumococcal Sequence Cluster (GPSC) 6 and harbored the virulence-associated rlrA islet, with co-trimoxazole-resistance mutations in folA and folP genes. Two ST162 strains with different serotypes 24F and 24B from the same patient were phylogenetically indistinguishable, showing that these strains were derived by serotype conversion during infection.

CONCLUSION

The recent changes in predominant STs were similar to those previously reported throughout Japan, except Tokyo. Little correlation between whole-genome phylogeny and serotypes and the observed serotype conversion in one patient indicate potentially variable immunogenicity of this serogroup.

Invasive pneumococcal disease caused by non-vaccine Streptococcus pneumoniae serotype 24B in an immunocompetent child

Invasive pneumococcal disease typically occurs in immunocompromised patients, although some vaccine strains of Streptococcus pneumoniae have been reported to cause invasive pneumococcal disease in immunocompetent vaccine recipients. In this study, we presented a case of a 16-month-old immunocompetent patient with lung abscess and empyema caused by nonvaccine S. pneumoniae serotype 24B. A consolidation occupying the right upper lobe in the chest computed tomography results, as observed at presentation, changed to thick-walled cavitary lesions at the end of a month of intravenous antibiotics, and antibiotics were continued for a total of two months. To the best of our knowledge this is the first report that focuses on the risk of invasive pneumococcal disease caused by S. pneumoniae serotype 24B in an immunocompetent child.