Epidemiological Profile of Causative Agents in Nosocomial Pneumonia: A Four- Year Multicenter Surveillance Study from Georgia (2020-2023)

Background Nosocomial pneumonia (NP), including hospital-acquired (HAP) and ventilator-associated pneumonia (VAP), remains a leading cause of morbidity, mortality, and antimicrobial resistance worldwide. Data from Eastern Europe and the Caucasus are scarce, limiting region-specific infection control strategies. Methods We conducted a prospective multicenter surveillance study across five tertiary hospitals in Georgia from May 2020 to December 2023. A total of 484 respiratory specimens were obtained from 397 adult patients with microbiologically confirmed NP. Pathogen identification was performed using culture and MALDI-TOF MS, with antimicrobial susceptibility testing according to CLSI guidelines. PCR assays detected major resistance genes. Epidemiological, molecular, and clinical outcomes were analyzed, including trends over time and ICU versus non-ICU differences. Results Gram-negative bacteria predominated (71.7%), with Pseudomonas aeruginosa (41.9%) as the leading pathogen, followed by Staphylococcus aureus (21.3%), Acinetobacter baumannii (13.4%), Klebsiella pneumoniae (13.0%), and Streptococcus pneumoniae (9.3%). Multidrug resistance (MDR) was identified in 80% of isolates, extensively drug-resistant (XDR) phenotypes in 18.4%, and pandrug-resistant (PDR) phenotypes in 1.4%. ESBL prevalence increased from 48.3% in 2020 to 79.8% in 2023 (p < 0.001), carbapenemase expression doubled from 15.0% to 30.2% (p < 0.01), and colistin resistance rose from 2.5% to 8.5% (p < 0.05). ICU isolates showed significantly higher MDR and XDR rates compared to non-ICU settings (p < 0.001). Thirty-day mortality correlated with resistance phenotype, ranging from 18.2% in susceptible infections to 71.4% in PDR cases. Conclusions This four-year surveillance study demonstrates alarming levels of antimicrobial resistance among NP pathogens in Georgia, with rising ESBL, carbapenemase, and colistin resistance, particularly in ICU settings. These findings highlight the urgent need for enhanced antimicrobial stewardship, infection prevention, and genomic surveillance strategies to contain the spread of high-risk clones and improve patient outcomes in resource-limited settings.