Is Polymicrobial Bacteremia an Independent Risk Factor for Mortality in Acinetobacter baumannii Bacteremia?

Abstract

This retrospective observational study assessed the differences between monomicrobial and polymicrobial A. baumannii bacteremia and identified possible independent risk factors for 14-day mortality. There were 379 patients with A. baumannii bacteremia admitted to a tertiary care center in northern Taiwan between August 2008 and July 2015 enrolled for data analysis. Among them, 89 patients (23.5%) had polymicrobial bacteremia and 290 patients (76.5%) had monomicrobial bacteremia. No significant difference in 14-day mortality was observed between patients with monomicrobial and polymicrobial A. baumannii bacteremia (26.9% vs. 29.2%, p = 0.77). Logistic regression controlled for confounders demonstrated that polymicrobial bacteremia was not an independent predictor of mortality, whereas appropriate antimicrobial therapy was independently associated with reduced mortality. Higher 14-day mortality rates were observed in the polymicrobial bacteremic patients with concomitant isolation of Escherichia coli, Pseudomonas aeruginosa, and Enterobacter spp. from the bloodstream. Compared with patients with monomicrobial multidrug-resistant A. baumannii (MDRAb) bacteremia, those with MDRAb concomitant with Gram-negative bacilli bacteremia had a worse outcome. Polymicrobial A. baumannii bacteremia was not associated with a higher 14-day mortality rate than that of monomicrobial A. baumannii bacteremia, although more deaths were observed when certain Gram-negative bacteria were concomitantly isolated. Appropriate antimicrobial therapy remains an important life-saving measure for A. baumannii bacteremic patients.

Keywords: Acinetobacter baumannii; appropriate therapy; bacteremia; mortality; polymicrobial infection.

Figure 1

Kaplan–Meier plot showing the survival rates of patients with acquired monomicrobial Acinetobacter baumannii (Ab) bacteremia, polymicrobial Ab bacteremia with concomitant Gram-negative bacilli (GNB), and polymicrobial Ab bacteremia with concomitant Gram-positive cocci (GPC) (polymicrobial Ab bacteremia with concomitant GNB versus monomicrobial Ab bacteremia, p = 0.098 by log-rank test; polymicrobial Ab bacteremia with concomitant GPC versus monomicrobial Ab bacteremia, p = 0.265 by log-rank test).

Figure 2

Kaplan–Meier plot showing the survival rates of patients with acquired polymicrobial multidrug-resistant Acinetobacter baumannii (MDRAb) bacteremia with concomitant Gram-negative bacilli (GNB), polymicrobial Ab bacteremia with concomitant Gram-positive cocci (GPC), and those with acquired monomicrobial MDRAb bacteremia. p-values were calculated by log-rank tests. (polymicrobial MDRAb bacteremia with concomitant GNB versus polymicrobial MDRAb bacteremia with concomitant GPC, p = 0.009 by log-rank test).