Predominant Pneumococcal Serotypes in Isolates Causing Invasive Disease in a Spanish Region: An Examination of Their Association with Clinical Factors, Antimicrobial Resistance, and Vaccination Coverage

Background: Streptococcus pneumoniae (S. pneumoniae) remains a leading cause of morbidity and mortality, particularly among vulnerable populations. This study investigates the epidemiology of pneumococcal serotypes associated with invasive pneumococcal disease (IPD) in the Comunidad Valenciana (CV) region, Spain, analysing 1587 isolates collected from 2014 to 2023. Methods: Serotyping and antimicrobial susceptibility testing were performed, and whole-genome sequencing was conducted on 104 isolates to explore their clonal relationships. Results: The most prevalent serotype was serotype 8 (17.5%), followed by serotype 3 (14.7%), with a notable increase in serotype 8 cases from 2019 onwards and a decline in serotype 19A being observed. Age distribution played a role, as serotype 8 was more frequent in individuals over ten years old. The overall recovery rate was 72%, while serotypes 3 and 15A exhibited the highest mortality rates. The vaccination coverage was highest among children under five, underscoring the need for continued surveillance to evaluate vaccine effectiveness. The antimicrobial resistance was most pronounced for erythromycin (20%) and clindamycin (16%), with serotypes 19A and 6C displaying the highest resistance levels. Whole-genome sequencing identified sequence type (ST) 53 and ST180 as the predominant STs for serotypes 8 and 3, respectively, mirroring global trends. Conclusions: These findings emphasize the necessity of continuous monitoring to inform vaccination policies and antimicrobial strategies, to ensure effective disease control and improved patient outcomes.