Characteristics of pneumococcal isolates
During the study period, a total of 474 S. pneumoniae isolates were collected, with 66.9% derived from male patients and 33.1% from females. Patients aged 70 years and older accounted for the largest proportion (35.7%) among all age groups. Most isolates were obtained from non-invasive specimens (89.2%), while 10.8% were from invasive sources such as blood and cerebrospinal fluid. Table S1 presents the basic characteristics of S. pneumoniae isolates, categorized into invasive and non-invasive types, with invasive strains detected across all five regions. Geographically, most isolates were collected from northern China (46.2%), followed by the western (23.9%), eastern (15.6%), southern (11.0%), and central (3.4%) regions (Table 1, Fig. 1).
Distribution of 20 general hospitals included in the study
Serotype distribution
The serotype distribution of the isolates is presented in Table 2. Overall, serotype 19F was the most prevalent (24.9%), followed by 19A (10.3%), 23F (9.5%), 6A (5.9%), and 15A (5.3%) (Figs. 2 and 3). Across all age groups, 19F remained the predominant serotype, ranging from 16.9% (50–59 years) to 30.2% (≥ 70 years). Similarly, 19F was the most prevalent serotype across all geographic regions, ranging from 22.4% (northern) to 31.2% (central). In the eastern and western regions, 19A was the second most common serotype, accounting for 16.2% and 13.3% of isolates, respectively, whereas in the southern, northern, and central regions, 23F ranked second (13.5%, 9.6%, and 12.5%, respectively). Serotype 19F maintained dominance in both invasive and non-invasive specimens, with respective prevalence rates of 27.5% and 24.6%. Notably, among invasive isolates, serotype 6A (11.8%) emerged as the secondary variant, closely trailing 19F. The proportion of serotype 33F, a PCV20-nonPCV13 serotype, was significantly higher in the invasive group (3.9%) compared to the non-invasive group (0.2%) (P < 0.05) (Table S2). A parallel pattern was observed in older adults (60–69 years), where 19F retained prominence at 16.9%, while 6A constituted the second most prevalent serotype (11.3%).
Serotype distribution of S.p isolates
Serotype distribution of S.p isolates
Vaccine coverage across different groups is presented in Table 3. Among all isolates, PCV20 demonstrated the highest overall coverage (69.4%), followed by PPV23 (65.4%), PCV15 (MSD) (63.7%), and PCV13 (62.9%). PCV21 had the lowest coverage (36.1%), while 18.6% of isolates were not covered by any of the evaluated vaccines. Across all age groups, PCV20 consistently showed the highest coverage, ranging from 67.6% (60–69 years) to 72.5% (50–59 years). Regionally, PCV20 had the highest coverage in all areas except the central region, where PPV23 coverage (75.0%) was the highest. Similarly, PCV20 demonstrated the greatest coverage in both invasive (80.4%) and non-invasive (68.1%) specimens.
Antibiotic resistance profiles of S. pneumoniae across regions
Antibiotic resistance among S. pneumoniae isolates from hospitalized adult patients in China was notably high, with multidrug resistance (MDR) detected in 94.06% of cases (Fig. 4). Resistance to macrolides was particularly widespread, with over 90% of isolates exhibiting resistance to erythromycin, azithromycin, and clarithromycin. Similarly, high resistance rates were observed for tetracycline (89.64%) and clindamycin (87.92%). Penicillin resistance was observed in 57.14% of isolates from meningitis cases and 45.81% of those from oral treatment cases. In comparison, resistance to third-generation cephalosporins was lower: ceftriaxone resistance was 28.57% in isolates associated with meningitis and 15.67% in non-meningitis cases. Resistance to trimethoprim-sulfamethoxazole was moderate (58.05%), whereas resistance to amoxicillin (16.70%) and chloramphenicol (8.44%) remained relatively low. Fluoroquinolone resistance was rare, and no resistance to vancomycin was detected.
Antibiotic resistance of S. pneumoniae by regions
Regional variations were evident in antibiotic resistance patterns. Macrolide and tetracycline resistance were consistently high across all regions, while β-lactam resistance varied. Notably, the East and West regions exhibited higher resistance rates for several antibiotics, whereas resistance to ceftriaxone (meningitis) was lowest in the East and highest in the West. Chloramphenicol resistance was highest in the Central region. The detailed distribution of antibiotic resistance rates across different regions is shown in Table 4. The comparison of antibiotic resistance profiles between invasive and non-invasive isolates is summarized in Table 5.
Antibiotic resistance profiles of S. pneumoniae by vaccine types
Antibiotic resistance patterns differed between invasive and non-invasive S. pneumoniae isolates (Fig. 5). Overall, multidrug resistance (MDR) was highly prevalent in both groups, with slightly higher resistance rates observed in non-invasive isolates (94.29%) compared to invasive isolates (92.16%). Resistance to macrolides, including erythromycin, azithromycin, and clarithromycin, was consistently high, exceeding 90% in both invasive and non-invasive isolates. Tetracycline resistance was also substantial, reaching 96.08% in invasive isolates and 91.92% in non-invasive isolates. Clindamycin resistance followed a similar trend, with rates of 82.35% and 88.60% in invasive and non-invasive isolates, respectively.
Antibiotic resistance of S. pneumoniae by disease category
For β-lactam antibiotics, cefaclor resistance was higher in non-invasive isolates (65.88%) than in invasive isolates (49.02%). Trimethoprim-sulfamethoxazole resistance was similar between the two groups (49.02% vs. 59.14%). When stratified by clinical syndrome and invasiveness, penicillin resistance was notably higher among isolates associated with meningitis—57.14% in invasive strains and 55.45% in non-invasive strains—compared to significantly lower resistance rates among non-meningitis-associated isolates (2.27% in invasive strains and 3.08% in non-invasive strains). Resistance to third-generation cephalosporins also varied: cefuroxime resistance was 39.22% in invasive isolates and 49.76% in non-invasive isolates, while ceftriaxone resistance among meningitis-related strains was 28.57% in invasive and 47.87% in non-invasive isolates. Fluoroquinolone resistance remained low, with levofloxacin resistance below 5% and moxifloxacin resistance nearly absent. Vancomycin resistance was not detected in any isolate.
When stratified by vaccine serotype coverage, resistance rates varied across pneumococcal vaccines (PCV13, PCV15, PCV20, PCV21, and PPV23) (Fig. 6). Serotypes covered by the higher-valency vaccines (PCV20 and PCV21) tended to exhibit higher resistance to macrolides, tetracyclines, and clindamycin, suggesting that resistant strains are more likely to be found within these serotypes. Penicillin resistance, particularly in meningitis-associated strains, remained moderate among serotypes covered by different vaccine formulations, while resistance to fluoroquinolones and vancomycin was consistently low across all vaccine serotype groups. Antibiotic resistance patterns among isolates stratified by vaccine coverage (PCV13, PCV15, PCV20, PCV21, PPV23) are presented in Table 6.
Antibiotic resistance of S. pneumoniae by vaccine types