Bloodstream Infections Due to Wild-Type Pseudomonas aeruginosa: Carbapenems and Ceftazidime/Avibactam Prescription Rate and Impact on Outcomes.

Background: Pseudomonas aeruginosa is one of the major concerns among bacterial diseases even when it shows a wild-type susceptibility pattern. In 2020, EUCAST reconsidered antibiogram interpretation shifting "I" from "intermediate" to "sensible, increased exposure" with possible significant impact on antibiotic prescription. The aim of this study was to evaluate mortality in patients with P. aeruginosa bloodstream infections treated with antipseudomonal penicillins or cephalosporins vs. carbapenems and ceftazidime/avibactam.

Methods: This is a retrospective observational study. All the patients with a bloodstream infection due to P. aeruginosa admitted to our hospital were enrolled. Exclusion criteria were as follows: extremely critical conditions, age <18 years, pregnancy, isolation of a strain non-susceptible to piperacillin/tazobactam and antipseudomonal cephalosporins. Patients were divided into group A (treatment with carbapenems or ceftazidime/tazobactam) and group B (treatment with antipseudomonal penicillin or cephalosporins).

Results: We enrolled 77 patients, 56 and 21 in groups A and B, respectively. The two groups were homogeneous for age, sex, and biochemical and clinical characteristics at admission. All-cause in-hospital mortality was 17/56 (30.4%) and 3/21 (14.3%) in groups A and B, respectively (p > 0.1). In group A, in-hospital BSI-related mortality was 23.2% (13/56), while it was 14.3% (3/21) in group B (p > 0.1). After multivariate analysis, only the PITT score represented a risk factor for BSI-related mortality (OR 2.917, 95% CI 1.381-6.163).

Conclusions: Both all-cause and BSI-related mortality were comparable between the two groups. Treatment with carbapenem or ceftazidime/avibactam did not represent a protective factor for mortality in wild-type P. aeruginosa BSI.