Distribution and Antibiotic Resistance of Pathogens in Bloodstream Infections Among Elderly Patients in Sichuan Province (2020–2024)

Objective: To characterize the distribution and antimicrobial resistance patterns of pathogens causing bloodstream infections in elderly patients in Sichuan Province from 2020 to 2024. Methods: Non-duplicate isolates from blood of patients aged ≥ 65 years in 134 provincial medical institutions (113 tertiary, 21 secondary) were collected and tested per a unified protocol. Species identification and susceptibility were interpreted using CLSI M100 criteria. Data were analyzed with WHONET 5.6. The study period was stratified into pandemic (2020– 2022) and post-pandemic (2023– 2024) phases to assess effects on multidrug-resistant and pandrug-resistant organisms. Results: 65,603 isolates were obtained from elderly patients’ blood specimens, of which 23,350 (35.6%) were Gram-positive and 42,253 (64.4%) were Gram-negative. The five most frequently detected organisms were Escherichia coli (38.4%), Klebsiella pneumoniae (12.6%), Staphylococcus hominis (6.6%), Staphylococcus epidermidis (6.0%), and Staphylococcus aureus (5.8%). E. coli exhibited low carbapenem resistance (ertapenem 0.8%, imipenem 0.9%, meropenem 0.9%), whereas K. pneumoniae showed carbapenem resistance of 6.7– 8.4%. Methicillin-resistant S. aureus and methicillin-resistant coagulase-negative staphylococci were detected at rates of 29.1% and 70.8%, respectively; no vancomycin-resistant staphylococci were identified. A total of 126 pandrug-resistant Acinetobacter baumannii (PDR-AB) isolates were identified, accounting for 11.2% (126/1124). No pandrug-resistant Enterobacterales or Pseudomonas aeruginosa were detected. In the post-pandemic period, the detection rates of carbapenem-resistant A. baumannii and carbapenem-resistant Klebsiella pneumoniae increased significantly compared with the pandemic period (P < 0.05). Conclusion: From 2020 to 2024, a diverse spectrum of bacterial species was isolated from bloodstream infections in elderly patients in Sichuan Province. Following the COVID-19 pandemic, the burden of carbapenem-resistant organisms increased. Region-specific antimicrobial resistance surveillance and strengthened in-hospital infection control are essential to guide appropriate antibiotic use and to curb the spread of resistant organisms.