Clinical Implications of Bacteremia Caused by Non-baumannii Acinetobacter Compared with Those of Acinetobacter baumannii Bacteremia

<b>Objectives:</b> This study aimed to compare clinical characteristics, antimicrobial susceptibility, and 28-day mortality between patients with <i>Acinetobacter baumannii</i> bacteremia (ABB) and non-<i>baumannii Acinetobacter</i> bacteremia (NBAB) after rapid matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) species identification. <b>Methods:</b> We retrospectively reviewed the clinical data of adult ABB and NBAB patients over >7 years. Multivariate logistic regression was used to identify the risk factors for 28-day mortality. <b>Results:</b> Of 273 episodes of <i>Acinetobacter</i> species bacteremia, 224 (82.1%) were ABB and 49 (17.9%) were NBAB. NBA isolates were predominantly <i>A. nosocomialis</i> (49%), with smaller proportions of <i>A. bereziniae</i>, <i>A. junii</i>, <i>A. ursingii</i>, and others. The primary sites of infection in NBAB cases were the intra-abdomen, urinary tract, intravascular catheters, and lungs. While only 4.0% of <i>A. baumannii</i> isolates were susceptible to carbapenem, 87.8% of non-<i>baumannii Acinetobacter</i> isolates were susceptible. Multivariate analysis revealed that low carbapenem resistance was independently associated with NBAB. Additionally, a higher Pitt bacteremia score, septic shock, continuous renal replacement therapy, inappropriate empirical antibiotic therapy, and thrombocytopenia were independent risk factors for the 28-day mortality in patients with ABB. <b>Conclusions:</b> Although less common than ABB, NBAB cases are increasing and exhibit lower carbapenem resistance. Rapid MALDI-TOF MS identification enables timely and appropriate antibiotic treatment. The key factors driving the 28-day mortality include illness severity, septic shock, renal replacement therapy, inappropriate antibiotics, and thrombocytopenia, highlighting the need for early risk assessments and tailored management. Ongoing surveillance and species-specific strategies are essential for combating resistant <i>Acinetobacter</i> infections.