Distribution of serotypes and antibiotic resistance profiles of Streptococcus pneumoniae in hospitalized adult patients: A retrospective multicenter surveillance in China (2018-2019)

Background: Streptococcus pneumoniae ( S. pneumoniae ) remains a major cause of community acquired pneumonia (CAP), particularly among older adults. In China, pneumococcal infections pose a substantial disease burden, with rising antibiotic resistance. Although vaccines have effectively reduced disease worldwide, data on adult serotype distribution and resistance in China are scarce. This study investigates serotype patterns and antimicrobial susceptibility of S. pneumoniae among Chinese adults. Methods: We collected a total of 474 S. pneumoniae isolates from adult patients diagnosed with pneumococcal infections in 14 cities across five geographic regions of China between 2018 and 2019. Clinical specimens included sputum, blood, bronchoalveolar lavage fluid (BALF), cerebrospinal fluid (CSF), pharyngeal and nasal swabs, and middle ear fluid. Minimum inhibitory concentrations (MICs) of antimicrobial agents were determined using the agar dilution method. Pneumococcal serotyping was performed using the Pneumotest-Latex kit and type-specific antisera. Results: Serotype 19F was the most prevalent across all age groups, specimen types, and regions. 20-valent pneumococcal conjugate vaccine (PCV20) is expected to provide the highest serotype coverage (69.4%) among all vaccines evaluated. Multidrug resistance was detected in over 94% of isolates, with high resistance to macrolides, tetracycline, and clindamycin. β-lactam resistance varied by syndrome and region. Non-invasive isolates showed slightly higher resistance than invasive ones. Serotypes covered by higher-valency vaccines were more likely to be antibiotic-resistant, although fluoroquinolone and vancomycin resistance remained low. Conclusions: Our findings highlight a high burden of antimicrobial resistance and predominance of specific serotypes, particularly 19F, among adult S. pneumoniae isolates in China. The broad serotype coverage of PCV20 suggests its potential advantage in future adult immunization strategies. Continued surveillance of serotype distribution and resistance patterns is essential to inform vaccine policy and guide effective antibiotic use.