Clinical and Microbiological Analysis of Risk Factors for Mortality in Patients With Carbapenem-Resistant Acinetobacter baumannii Bacteremia

Abstract

Background: Carbapenem-resistant Acinetobacter baumannii (CRAB) infection is associated with significant mortality, causing worldwide concern, yet there are limited data on contributing microbiological factors. This study aimed to identify the clinical and microbiologic risk factors for mortality in CRAB bacteremia.

Methods: Adult patients with monomicrobial CRAB bacteremia in a 2700-bed tertiary hospital between December 2012 and December 2018 were retrospectively enrolled. Risk factors for 30-day mortality were evaluated. All isolates collected on the first day of bacteremia were subjected to colistin susceptibility testing by broth microdilution and to genotyping by multilocus sequence typing.

Results: A total of 164 patients were enrolled, and 90 (55%) died within 30 days. The most common genotype among the isolates was ST191 (49%), and 12 isolates (7%) were resistant to colistin. Genotype, colistin minimum inhibitory concentration, and colistin resistance were not significantly associated with mortality, in contrast to several clinical factors. In multivariable analysis, ineradicable or not-eradicated focus (adjusted odds ratio [aOR], 4.92; 95% CI, 1.95-12.42; P = .001), septic shock (aOR, 4.72; 95% CI, 2.12-10.49; P < .001), and inappropriate antimicrobial therapy (aOR, 2.54; 95% CI, 1.05-6.16; P = .04) were independent risk factors for mortality. Among antibiotic strategies, colistin combined with tigecycline or other antibiotics were significantly associated with lower mortality after adjustment for confounding factors.

Conclusions: Clinical factors such as the nature of the infection source and source control, severity of bacteremia, and appropriateness of antibiotics, rather than microbiological factors, contribute to mortality in CRAB bacteremia. A specific antibiotic combination may help improve outcomes.

Keywords: Acinetobacter baumannii; bacteremia; carbapenems; mortality; multidrug-resistant; risk factors.

Figure 1.

Thirty-day mortality according to (A) colistin minimum inhibitory concentration and (B) genotype of carbapenem-resistant Acinetobacter baumannii blood isolates. Abbreviation: MIC, minimum inhibitory concentration.