Demographic characteristics
From January 1, 2016 to December 3, 2018, 1161 patients (<18 years old) with PBM were enrolled for screening. In accordance with the exclusion criteria, 1142 confirmed PBM patients were ultimately included. Less than half of the enrolled patients were boys (501/1142), and the median age was 3 months (range: 0 days to 17 years, 7 months). Up to 65.9% of patients were < 1 year old, 44.9% were < 3 months old, and a sharp decline in the percentage was observed with increasing age.
Pathogen composition
A total of 1193 bacterial pathogens were obtained from 1142 patients. Gram-positive organisms accounted for nearly 69.6% (830/1193) of the isolates, and 30.4% (363/1193) were gram-negative organisms. The three leading pathogens causing PBM were Staphylococcus epidermidis (S. epidermidis) (197/1193; 16.5%), E. coli (148/1193; 12.4%) and S. pneumoniae (127/1193; 10.6%), followed by Enterococcus faecium (E. faecium) (115/1193; 9.6%), Staphylococcus hominis (S. hominis) (85/1193; 7.1%), group B Streptococcus (GBS) (59/1193; 4.9%), Staphylococcus haemolyticus (S. haemolyticus) (42/1193; 3.5%), Klebsiella pneumoniae (K. pneumoniae) (40/1193; 3.4%), S. aureus (39/1193; 3.3%), and Acinetobacter baumannii (A. baumannii) (27/1193; 2.3%) (Table 1).
Distribution of major PBM pathogens according to age and clinical ward
The spectrum of pathogens causing PBM was highly variable in children of different ages (Figure 2). In infants under 3 months of age, the top 3 pathogens were E. coli (116/523; 22.2%), E. faecium (75/523; 14.3%), and S. epidermidis (57/523; 10.9%). However, in children more than 3 months of age, the top 3 pathogens were S. epidermidis (140/670; 20.9%), S. pneumoniae (117/670; 17.5%), and S. hominis (57/670; 8.5%). As shown in Figure 2, the other prevalent bacteria also varied by age group. Children less than one year old had the greatest abundance of pathogenic species, the leading pathogen among which was E. coli (134/776; 17.3%), followed by S. epidermidis (105/776; 13.5%) and E. faecium (88/776; 11.3%).
In terms of clinical ward distribution, these common pathogens were detected in the pediatric intensive care unit (PICU), surgical department and other departments (Additional file 1: Figure S1). S. epidermidis was detected more commonly in the surgical department (31.1%) than in the PICU (10.8%) and other departments (13.9%) (P <0.001). However, E. coli, S. pneumoniae, E. faecium, and GBS were detected more frequently in the PICU and in the other departments than in the surgical department (all P <0.05).
AMR patterns of the major gram-positive bacteria
As shown in Table 2, the three main species of coagulase-negative Staphylococcus (CoNS), namely, S. epidermidis, S. hominis and S. haemolyticus, were isolated from CSF cultures. The resistances of these isolates to penicillin (PEN) and erythromycin (ERY) were greater than 71.0%. Resistance to methicillin depended on oxacillin (OXA) resistance. Therefore, the overall detection rate of the methicillin-resistant CoNS (MRCoNS) isolates was approximately 80.0% and declined from 80.5% in 2016 to 72.3% in 2018 (Figure 3). All of these three species were susceptible to linezolid (LNZ) (100%) and vancomycin (VAN) (100%). Over 65.0% of the isolates, except S. haemolyticus, were also susceptible to aminoglycosides, fluoroquinolones, co-trimoxazole (SXT), rifampin (RIF) and tetracycline (TET). For S. pneumoniae isolates, resistance to fluoroquinolones, LNZ, or VAN was not detected in this study. The susceptibility to amoxicillin (AMX), cefotaxime (CTX) and ceftriaxone (CRO) was 74.8%, 59.0%, and 50.0%, respectively. However, over 84.0% of the S. pneumoniae isolates were resistant to ERY, clindamycin (CLI), SXT, and TET. The resistance of S. pneumoniae isolates to PEN was 82.8%, increasing from 75.0% in 2016 to 87.5% in 2018 (Figure 3). More than 95.0% of E. faecium isolates showed susceptibility to VAN, LNZ, and tigecycline (TGC), but the resistance rates to other antibacterial drugs were over 62.9%.
AMR patterns of the major gram-negative bacteria
As shown in Table 3, more than 93.0% of the E. coli isolates were sensitive to cefoxitin (FOX), piperacillin/tazobactam (TZP), cefoperazone/sulbactam (CSL), amikacin (AMK) and carbapenems, and the resistance rates for ampicillin (AMP) and piperacillin (PIP) exceeded 82.0%. The sensitivities of E. coli to third-generation cephalosporins, aztreonam and fluoroquinolones were 47.6-73.6%, 65.3%, 44.3-46.4%, respectively. Moreover, the detection rate of ESBL-producing E. coli was stable and fluctuated between 44.4% and 49.2% in 2016-2018. The proportion of carbapenem-resistant E. coli (CRECO) isolates was 5.0%, increasing from 2.2% in 2016 to 9.1% in 2018 (Figure 3). K. pneumoniae isolates exhibited susceptibility rates greater than 50.0% to aminoglycosides, fluoroquinolones, TET, SXT, IMP, and ETP, but the resistance rates to other antibiotics were greater than 50.0%. The proportions of ESBL-producing K. pneumoniae and carbapenem-resistant K. pneumoniae (CRKP) were 74.3% and 54.5%, respectively. The data from 2016 to 2018 demonstrated that ESBL-producing K. pneumoniae and CRKP showed an upward trend (Figure 3).
For A. baumannii and P. aeruginosa isolates, the susceptibility rates of A. baumannii isolates to aminoglycosides and fluoroquinolones exceeded 55.0%. The susceptibility of isolates to cephalosporins and carbapenems ranged from 37.5% to 66.7% and 45.5% to 68.4%, respectively. The susceptibility rates of P. aeruginosa isolates to PIP, third-generation cephalosporins, TZP, aminoglycosides, fluoroquinolones, and carbapenems were greater than 60.0%, but the resistance of isolates to AMP and ampicillin/sulbactam (SAM) exceeded 92.0%.