Pseudomonas aeruginosa in patients with Nosocomial Respiratory Infections: A secondary analysis of the European Network for ICU-Related Respiratory Infections (ENIRRIs)

Background: Nosocomial respiratory infections (NRIs) are the most common complication among ICU patients, with Pseudomonas aeruginosa frequently identified. However, its global prevalence and associated risk factors remain unclear. Research question: Among ICU patients with NRI, what is the international prevalence of P. aeruginosa, and which clinical factors are associated with an increased risk? Study design and methods: This secondary analysis used data from the European Network for ICU-Related Respiratory Infections (ENIRRI), a prospective cohort study conducted across 12 countries from May 2016 to August 2019. Data from 1,059 NRI patients who underwent microbiological testing were analyzed. Descriptive statistics, imputation of missing data, LASSO regression, Elastic Net, Random Forest, and multivariable logistic regression were applied. Model performance was assessed using McFadden's R2 and the Hosmer-Lemeshow test. Results: The median patient age was 64 years (IQR 49-73), and 72% were male. Pathogens were identified in 67% (710/1059) of cases, primarily using blood cultures (78%). P. aeruginosa was detected in 14.5% (n=153), with antimicrobial resistance mechanisms in 5.1% (n=55). Among these, 19.6% were multidrug-resistant and 11.1% produced carbapenemase. The highest prevalence was observed in Germany, Argentina, and France. Ventilator-associated pneumonia (VAP) was the predominant diagnosis, accounting for 66% of P. aeruginosa cases. Septic shock and acute kidney injury were the most frequent complications. No significant mortality differences were found between patients with and without P. aeruginosa. Key risk factors included COPD Gold D, autoimmune disease, chronic kidney disease, and acute kidney injury on day 1. Interpretation: P. aeruginosa is a leading NRI pathogen, with prevalence varying across countries. A high proportion of patients received empirical anti-Pseudomonas treatment without confirmed infection by P. aeruginosa. Key risk factors identified for Pseudomonas NRI were COPD Gold D, autoimmune disease, chronic kidney disease, and acute kidney injury. These findings support the need for more personalized, evidence-based empirical therapy.