Bacteremic nosocomial pneumonia caused by Gram-negative bacilli: results from the nationwide ALARICO study in Italy

Abstract

Purpose: To describe the clinical characteristics and outcomes of patients with nosocomial pneumonia (NP) caused by carbapenem-resistant Gram-negative bacilli (CR-GNB) and to compare them to patients with NP caused by carbapenem-susceptible (CS)-GNB.

Methods: Prospective observational multicenter study including patients with bacteremic NP caused by GNB from the ALARICO Network (June 2018-January 2020). The primary outcome measure was 30-day mortality. A Cox regression analysis was performed to identify factors independently associated with 30-day mortality. Hazard ratio (HR) and 95% confidence intervals (CI) were calculated.

Results: Overall, 167 patients with GNB NP were included: 101 with bacteremic NP caused by CR-GNB (n = 39 by KPC-producing Klebsiella pneumoniae, n = 29 by carbapenem-resistant Acinetobacter baumannii, n = 28 by carbapenem-resistant Pseudomonas aeruginosa, n = 5 by MBL-producing Klebsiella pneumoniae) and 66 cases of bacteremic CS-GNB NP. Thirty-day mortality rate was higher in patients with NP caused by CR-GNB compared to those with NPcaused by CS-GNB (46.5% vs 30.3%, p = 0.036). On multivariable analysis, age (HR 1.044, 95% CI 1.021-1.067, p < 0.001), hematological malignancy (HR 4.307, 95% CI 1.924-9.643, p < 0.001) and septic shock (HR 3.668, 95% CI 2.001-6.724, p < 0.001) were factors independently associated with 30-day mortality, while the receipt of adequate antibiotic therapy within 24 h from infection onset (HR 0.495, 95% CI 0.252-0.969, p = 0.04) was a protective factor. Carbapenem resistance was not associated with increased risk of mortality (HR 1.075, 95% CI 0.539-2.142, p = 0.837).

Conclusions: Patients with bacteremic NP caused by CR-GNB have high mortality rate. Strategies to reduce the time from infection to the administration of adequate antibiotic therapy should be implemented in patients with NP.

Keywords: Acinetobacter baumannii; Klebsiella pneumoniae; Pseudomonas aeruginosa; Carbapenem-resistance; Gram-negative bacilli; Multidrug resistance.