Clinical characteristics and treatment outcomes of Acinetobacter baumannii bloodstream infections in a setting with high carbapenem susceptibility among isolates.

Abstract

In most settings, carbapenem-resistant Acinetobacter baumannii (CRAB) infections predominate over carbapenem-susceptible Acinetobacter baumannii (CSAB). Treatment guidelines focus on the management of CRAB and do not describe the optimal antibiotic choice for CSAB. We describe the clinical characteristics and outcomes in both CRAB and CSAB. We examined consecutive episodes of CRAB or CSAB bloodstream infections in our institution from February 2022 to July 2024. Clinical, laboratory, and microbiological data were tabulated, and adverse outcomes were defined as the need for intensive care (ICU) or all-cause in-hospital mortality. We compared (i) CRAB to CSAB, and among patients with CSAB, (ii) we evaluated if the definitive antibiotic choice was associated with adverse outcomes, after adjusting for C-reactive protein levels. We identified 71 unique episodes of bacteremia, of which a majority (52/71, 73.2%) were nosocomial onset. A minority were CRAB (15/71, 21.1%). These patients often had ICU onset, prior carbapenem exposure, and were more likely to experience mortality (73.3% versus 16.1%, P < 0.001). Only a minority of patients (7/71, 9.9%) received dual antibiotic therapy. Among the 56 patients with CSAB, only 11/56 (19.6%) experienced adverse outcomes. On multivariable analysis, after adjusting for elevated C-reactive protein, the use of carbapenems as the definitive antibiotic choice remained independently associated with adverse outcomes (adjusted odds ratio 7.34, 95% CI 1.25-43.01, P = 0.027). CSAB was far more common than CRAB in our setting. Prior carbapenem exposure and ICU onset were important risk factors for CRAB, which had higher mortality than CSAB. Carbapenem-sparing options may be considered as the definitive antibiotic choice for CSAB.

Importance: In our setting, carbapenem-susceptible Acinetobacter baumannii (CSAB, n = 56/71, 78.9%) bloodstream infections (BSIs) were far more common than with carbapenem-resistant isolates (CRAB). CRAB BSI was associated with intensive care onset, prior carbapenem use, and had higher mortality (73.3% versus 16.1%). In CSAB BSI, after adjusting for elevated C-reactive protein, the definitive use of carbapenems for treatment remained independently associated with adverse outcomes (adjusted odds ratio 7.34, 95%CI 1.25-43.01). These findings may suggest that carbapenem-sparing regimens may be effective alternative antibiotic choices for CSAB. Although treatment guidelines focus on CRAB, future prospective studies should also evaluate optimal treatment strategies for CSAB.