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 <18 y across 28 tertiary hospitals. 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. Plain Language Summary: Streptococcus pneumoniae is a bacterium that can cause serious infections in children, such as blood infections and meningitis. In Türkiye, vaccines against this bacterium have been used for more than 10 y. This study looked at children with these infections between January 2019 and April 2025 in 28 hospitals across the country. We found 203 children with infections, most of them around 4 y old. The most common illnesses were blood infections and meningitis. Almost half of the infections were caused by types of the bacterium that are already included in the current vaccine (PCV13), especially types 3, 14, 19F, and 19A. However, some infections were from other types, like 9N and 15A, which are not covered by the vaccine. Newer vaccines (such as PCV15 and PCV20) that protect against more types could prevent even more cases. Most of the bacteria were still sensitive to penicillin, which means this medicine usually works well. But resistance to another group of antibiotics, called macrolides, was very high–about 6 out of 10 cases. Overall, this study shows that the current vaccine is still valuable, but new vaccines and careful monitoring are needed to give children better protection and to guide doctors in choosing the best treatments.