Acinetobacter baumannii (Ab) is an important cause of healthcare-associated infections. Multilocus sequence typing (MLST) provides a highly discriminative typing method. We aimed to determine the clinical impact of Ab sequence types (ST) in patients with bloodstream infection (BSI).

Patients with Ab-BSI were followed prospectively from 2009 to 2014. We randomly selected one-third of non-duplicate bacteremic isolates for MLST and correlated the Ab ST with the clinical course. The primary outcome was all-cause in-hospital mortality.

We enrolled 148 patients. Seventy-seven (52.0%) of the isolates were ST2. Patients with ST2-BSI were less likely to be treated with appropriate empirical antimicrobial agents (31.1% vs. 60.6%; P < 0.001). They had greater mortality (66.2% vs. 40.8%; P = 0.003) than patients with non-ST2-BSI. In the multivariable analysis, ST2 independently predicted greater severity of infection (Pitt bacteremia score) (adjusted odds ratio (aOR), 3.38; 95% confidence interval (CI), 1.75–6.54; P < 0.001). Mediated by a higher Pitt bacteremia score (Sobel test P < 0.001), ST2 is an independent prognostic factor that predict mortality (aOR, 2.34; 95% CI, 1.07–5.11; P = 0.03).

ST2 was associated with high rates of inappropriate antimicrobial therapy, severe infection and mortality. Further studies are needed to confirm our findings and explore the potential of role of the virulence.