Serotype 38 Streptococcus pneumoniae emerges as one of the dominant serotypes causing invasive pneumococcal disease in Germany and Poland, but not in the Netherlands
Introduction Streptococcus pneumoniae is a major cause of community-acquired pneumonia and invasive pneumococcal disease (IPD). Vaccination prevents IPD by vaccine serotypes, but leads to an increase in disease caused by non-vaccine serotypes.  Aim We aimed to characterise serotype 38 isolates from IPD patients in Germany, Poland and the Netherlands to explain a recent surge in cases.  Methods IPD isolates were collected, serotyped and phenotypically tested for antimicrobial resistance by reference laboratories in Germany, Poland and the Netherlands. One hundred and thirty serotype 38 isolates were sequenced and subjected to phylogenetic analysis, along with 213 publicly-available genomes, and characterised according to their virulence factors and resistance genes.  Results Surveillance data from 2013/2014 to 2023/2024 revealed a steep increase in the percentage of serotype 38 in IPD in Germany and Poland in 2023/2024. This was most pronounced among children aged 0-4 years (from 4.3% to 17.1% and 4.0% to 15.8% of IPD cases, respectively) and adults aged >60 years (from 1.5% to 7.0% and from 0.7% to 2.9%, respectively). In the Netherlands the relative contribution remained stable. Phylogenetic analysis showed that recent isolates mostly emerged from previously circulating strains, carried little antimicrobial resistance genes, and showed no significant changes in gene content.  Conclusion The recent surge in non-vaccine serotype 38 among IPD cases in Germany and Poland cannot be explained by genetic or resistance changes. Our study underscores the importance of international collaboration in monitoring pneumococcal serotype trends, to assess vaccination impacts and inform policymakers.