Distribution of Isolated Pathogens and Resistance Patterns in Non-Ventilator Hospital-Acquired Pneumonia at King Hamad University Hospital (KHUH), Bahrain: A Retrospective Study

Background Non-ventilator hospital-acquired pneumonia (NV-HAP), defined as pneumonia developing ≥48 hours after admission in non-intubated patients, is increasingly recognized as a major contributor to hospital morbidity and mortality but remains under-studied compared with ventilator-associated pneumonia (VAP), particularly in the Gulf region. In Bahrain, published NV-HAP data are absent, limiting locally informed empiric therapy and antimicrobial stewardship. This study aimed to characterize bacterial pathogens causing culture-confirmed NV-HAP in adults at a tertiary center in Bahrain and to describe antimicrobial resistance patterns and temporal resistance trends. Materials and methods A retrospective cross-sectional study was conducted at King Hamad University Hospital (KHUH), Bahrain. Adult patients (≥18 years) with clinically and radiographically confirmed NV-HAP and positive sputum or bronchoalveolar lavage (BAL) cultures between January 2017 and March 2022 were included. NV-HAP required onset ≥48 hours after admission in non-intubated patients. Exclusion criteria included VAP, non-bacterial infections, prior antimicrobial therapy, restricted clinical trials, and immunocompromising conditions. ICD-10 code U69.01 was used for case identification, followed by manual chart review to confirm NV-HAP. Culture thresholds were >10⁴-10⁵ CFU/mL for sputum and >10³-10⁴ CFU/mL for BAL. Organism identification used MALDI-TOF, and susceptibility testing used the BD Phoenix M50 system. Multidrug resistance (MDR) was defined as non-susceptibility to ≥1 agent in ≥3 antimicrobial classes. Statistical analysis was performed using SPSS v25, with p ≤ 0.05 considered significant. Results Of 583 screened hospital-acquired pneumonia cases, 184 culture-confirmed NV-HAP cases met the inclusion criteria. Patients were predominantly male (65.2%) and elderly (≥75 years: 58.7%). Older patients had significantly higher comorbidity burdens (p < 0.01). Twenty bacterial species were identified; the most frequent pathogens were Klebsiella pneumoniae (38.59%), Pseudomonas aeruginosa (26.09%), Staphylococcus aureus (8.70%), Stenotrophomonas maltophilia (6.52%), and Acinetobacter baumannii (3.80%) (p = 0.014). K. pneumoniae was significantly more frequent in patients ≥ 75 years (44% vs 30%, p < 0.01). MDR was observed in 97.56% of K. pneumoniae isolates and was more common in older patients (p = 0.02). Resistance to ceftazidime, cefuroxime, levofloxacin, meropenem, and piperacillin-tazobactam increased significantly over time. P. aeruginosa showed expected intrinsic resistance patterns, with preserved susceptibility to aminoglycosides; MDR isolates comprised 14.6%. Discussion This first Bahrain NV-HAP study demonstrates a predominantly Gram-negative pathogen profile dominated by K. pneumoniae and P. aeruginosa, with low A. baumannii compared with regional VAP-focused studies, supporting distinct NV-HAP microbiology. The association between advanced age and K. pneumoniae, combined with high MDR rates and worsening resistance trends, has important implications for empiric therapy and antimicrobial stewardship. Conclusion NV-HAP in Bahrain is characterized by a high burden of MDR K. pneumoniae, particularly among elderly patients, and increasing resistance to commonly used agents. These findings highlight the need to revise empiric treatment strategies and strengthen antimicrobial stewardship, providing baseline data to guide NV-HAP management and regional surveillance.