Molecular Characterization of Streptococcus pneumoniae Strains Isolated from Patients with Invasive Infections in a Romanian Hospital.

Invasive pneumococcal disease (IPD) results from the dissemination of Streptococcus pneumoniae to normally sterile anatomical sites such as the bloodstream or cerebrospinal fluid. One of the primary roles of pneumococcal conjugate vaccines (PCVs) used in Romania is to reduce the burden of pneumococcal disease. This single-center retrospective study provides an updated overview of IPD epidemiology in a Romanian tertiary hospital. We analyzed 67 IPD cases identified between 2017 and 2023, of which 45 isolates underwent whole-genome sequencing followed by multilocus sequence typing. Results of genome sequence analysis revealed a diverse population of pneumococci, underlining the importance of continuous genomic surveillance. Expanded-valency pneumococcal conjugate vaccines (PCVs), particularly PCV20, showed markedly improved serotype coverage compared to PCV7 and PCV13, while PCV21 showed serotype coverage comparable to that of PCV13. Antimicrobial susceptibility testing revealed sustained resistance to beta-lactams, particularly among meningitis isolates, underscoring the need for targeted antibiotic stewardship and continuous monitoring of local resistance trends. Overall, these findings highlight the evolving epidemiology of invasive pneumococcal disease in Romania, in the post-PCV era, and the need to adapt vaccination and treatment strategies accordingly.