Serotype distribution of Streptococcus pneumoniae in children with invasive diseases in Türkiye, 2019–2025: An update in the 10th to 15th years of routine pneumococcal conjugate vaccination

Invasive pneumococcal disease (IPD) caused by Streptococcus pneumoniae remains a significant cause of pediatric morbidity. This study updates the serotype distribution and antibiotic resistance of pediatric IPD in Türkiye for 2019-2025, about a decade after 13-valent pneumococcal conjugate vaccine (PCV13) was introduced in the National Immunization Program. We conducted a multicenter, hospital-based prospective surveillance between January 2019-April 2025 in children S. pneumoniae isolates from sterile sites (blood, cerebrospinal fluid, pleural fluid) were confirmed by standard methods and serotyped using the Quellung reaction. Antimicrobial susceptibility was determined by gradient test as per CLSI criteria. A total of 203 samples were identified from 203 pediatric cases (median age 4 y, 56.2% boys). The clinical presentations were bacteremia/sepsis (57.6%) and meningitis (26.1%). The leading serotypes were 3 (14.3%), 14 (10.3%), 19F (7.9%), 19A (6.4%), 9N (4.4%), 15A (4.4%). PCV13 serotypes accounted for 46.8% isolates, while PCV7 and PCV10 serotypes were detected in 23.2% and 24.6%, respectively. Broader vaccines would increase coverage: PCV15 (46.8%) and PCV20 (56.7%). Antibiotic susceptibility (non-meningitis breakpoint) remained high for beta-lactams; 91.9% of isolates were penicillin-susceptible, with only 0.7% fully resistant, and cefotaxime resistance was rare (2.7%). Conversely, macrolide resistance was high, with 60.2% of isolates resistant to erythromycin. A decade after PCV13 implementation, vaccine serotypes - particularly 3, 14, 19F, and 19A - still cause nearly half of pediatric IPD, though non-vaccine serotypes such as 9N and 15A are rising. Higher-valent PCVs may improve protection, and continued surveillance is critical to guide vaccine policy and treatment strategies.