Invasive and Bronchoalveolar Lavage Isolates of Streptococcus pneumoniae in Türkiye

Overview

This multicenter laboratory study evaluates serotype distribution, antibiotic susceptibility, and potential vaccine serotype coverage among 462 Streptococcus pneumoniae isolates from adults in Türkiye. Serotype 3 predominates, and erythromycin nonsusceptibility increases over the study period. The findings suggest broader potential coverage with PCV20 than PCV13.

Background

S. pneumoniae causes invasive and noninvasive infections, with more serious disease in older adults, immunocompromised individuals, and people with underlying conditions. Pneumococcal vaccination reduces infections caused by vaccine serotypes, but persistent vaccine serotypes and changing serotype distributions highlight the importance of surveillance.

Data Highlights

• Researchers evaluated 462 isolates collected from January 2019 through August 2025 at 27 tertiary hospitals across 17 cities.

• Patients aged ≥65 years accounted for 43.9% of the study population.

• The most frequent serotypes were 3 (17.3%), 9N (9.1%), and 19F (5.4%).

• Potential serotype coverage was 34.6% for PCV13, 35.9% for PCV15, 47.8% for PCV20, and 59.5% for PPSV23.

• Using nonmeningitis breakpoints, penicillin susceptibility was 96.3% and cefotaxime susceptibility was 97.8%.

• Erythromycin nonsusceptibility increased from 33.3% in 2019 to 57.5% in 2025.

Key Findings

• Vaccine serotype coverage was significantly higher among isolates from patients aged ≥65 years than among those from younger adults.

• Coverage was significantly higher among invasive isolates than among bronchoalveolar lavage and tracheal aspirate isolates.

• PCV20 and PPSV23 covered significantly greater proportions of isolates than PCV13 and PCV15.

• No significant difference in serotype coverage was found between PCV13 and PCV15.

• Vaccine serotype coverage did not differ significantly across study years.

Interpretation

PCV20 offers broader potential serotype coverage than PCV13 among the studied isolates, particularly in older adults. These estimates describe the proportion of isolates belonging to vaccine serotypes rather than demonstrated vaccine efficacy.

Limitations

The study included only culture-positive cases, potentially biasing serotype representation. Clinical information was limited, and participants’ vaccination status was unavailable. Serotyping was incomplete for 78 isolates, which may have affected vaccine coverage estimates.

Clinical Implications

The findings may inform adult pneumococcal vaccination strategies in Türkiye. Increasing erythromycin nonsusceptibility reinforces the authors’ emphasis on prudent antibiotic use, while regional and temporal variation supports continued surveillance.

Conclusion

Serotype 3 remains the predominant serotype among the studied adult isolates. Broader potential coverage with PCV20 may support its consideration in adult vaccination strategies, especially for older adults. Continued serotype surveillance and rational antibiotic use remain essential.

Related Resources & Content

1. Expanded recommendations for use of pneumococcal conjugate vaccines among adults aged ≥50 years: recommendations of the Advisory Committee on Immunization Practices: United States, 2024 — Kobayashi M, Leidner AJ, Gierke R, et al. — MMWR Morbidity and Mortality Weekly Report, 2025;74(1):1–8.

2. Serotype distribution of Streptococcus pneumoniae and pneumococcal vaccine coverage in adults in Turkey between 2015 and 2018 — Hascelik G, Soyletir G, Gulay Z, et al. — Annals of Medicine, 2023;55(1):266–275.

3. Global distribution and characteristics of pneumococcal serotypes in adults — Maeda H, Morimoto K — Human Vaccines & Immunotherapeutics, 2025;21(1):2469424.

4. Non-invasive Streptococcus pneumoniae infections are associated with different serotypes than invasive infections, Belgium, 2020 to 2023 — Passaris I, Depickère S, Braeye T, et al. — Eurosurveillance, 2024;29(45):2400108.

5. Trends of serotypes and resistance among Streptococcus pneumoniae in the UK and Ireland (1999–2019) — Horner C, Reynolds R, Mushtaq S, et al. — Journal of Antimicrobial Chemotherapy, 2025;80(Supplement_4):iv72–iv86.