Clinical characteristics and risk factors for carbapenem-resistant Acinetobacter pittii infection: A retrospective study

Objective: To characterize the clinical features and identify independent risk factors for carbapenem-resistant Acinetobacter (A.) pittii (CRAP) infection, with particular attention to patients with hematological malignancies. Methods: We conducted a single-center retrospective study of 283 hospitalized patients with A. pittii isolates between May 2021 and December 2024. Independent risk factors were identified by univariate and multivariate backward stepwise logistic regression; a sensitivity analysis including all classifiable patients ( n =279) and that adjusted for colonization status was performed. In addition, all variables with univariate P <0.10 were entered simultaneously into a full multivariable model, and a 1:2 propensity score-matched cohort was constructed to assess the robustness of the findings. Results: A total of 283 patients with A. pittii isolates were included, comprising 101 in the carbapenem-resistant group and 182 in the susceptible group. Primary analysis was restricted to 202 patients with clinical infection (39 resistant, 163 susceptible). In the infection cohort, hematological malignancy (48.7% vs . 12.3%), hematopoietic stem cell transplantation (HSCT; 38.5% vs . 4.9%), chemotherapy (53.8% vs . 17.8%), glucocorticoid use (92.3% vs . 63.8%) and carbapenem exposure (64.1% vs . 31.3%) were significantly more common in the resistant group than in the susceptible group. Resistant isolates were highly resistant to meropenem (100%), piperacillin/tazobactam (97.1%) and imipenem (97.3%), but remained susceptible to amikacin (6.9% resistant), tigecycline (8.1% resistant) and cefoperazone/sulbactam (41.0% resistant). Multivariate analysis identified HSCT as an independent risk factor ( OR 8.19; 95% CI 2.94-22.82; P <0.001), with carbapenem exposure of marginal significance ( OR 2.26; 95% CI 0.99-5.15; P =0.05). The sensitivity analysis confirmed HSCT ( OR =4.67), hematological malignancy ( OR =2.68), glycopeptide exposure ( OR =2.13) and colonization itself ( OR =5.04) as independent predictors. In the propensity score-matched cohort (28 resistant vs . 56 susceptible), HSCT ( OR 3.89; 95% CI 1.29-11.76; P =0.02), glucocorticoid use ( OR 5.39; 95% CI 1.45-20.03; P =0.01), carbapenem exposure ( OR 3.26; 95% CI 1.27-8.38; P =0.01) and glycopeptide exposure ( OR 5.25; 95% CI 1.77-15.61; P =0.003) remained significantly associated with carbapenem resistance. Conclusions: HSCT is an independent risk factor for CRAP infection, and carbapenem exposure likely reflects underlying immunosuppression rather than an independent risk factor. Active surveillance, infection control and antimicrobial stewardship are warranted in patients with hematological malignancies.