Early prediction of carbapenem resistance phenotype in ICU-acquired Acinetobacter baumannii infection before susceptibility reporting: a temporally validated study.

OBJECTIVES: To develop and temporally validate an interpretable approach using routinely available clinical data to differentiate carbapenem-resistant from carbapenem-susceptible Acinetobacter baumannii in intensive care unit (ICU) patients before susceptibility reporting. METHODS: This single-center retrospective cohort study included 423 critically ill patients with confirmed A. baumannii infection (June 2022 to December 2025), temporally split into training (n = 317) and test (n = 106) cohorts. Predictors were selected via univariate screening, least absolute shrinkage and selection operator (LASSO) regression, and multivariable logistic regression. A logistic regression nomogram and an eXtreme Gradient Boosting (XGBoost) model were evaluated for discrimination, calibration, and clinical utility using decision curve analysis and SHapley Additive exPlanations (SHAP) interpretability. RESULTS: In the temporal test cohort, the logistic regression model achieved an area under the receiver operating characteristic curve (ROC-AUC) of 0.831 and an area under the precision-recall curve (PR-AUC) of 0.916, while the XGBoost model achieved an ROC-AUC of 0.878 and a PR-AUC of 0.936. Prior carbapenem exposure, Glasgow Coma Scale score, duration of mechanical ventilation, and Acute Physiology and Chronic Health Evaluation II (APACHE II) score were the major contributors identified by SHAP analysis. Decision curve analysis demonstrated net benefit across clinically relevant threshold probabilities (approximately 0.10-0.80). CONCLUSIONS: This study developed and temporally validated interpretable models for early differentiation of carbapenem resistance phenotype to inform empirical antimicrobial therapy and antimicrobial stewardship before definitive susceptibility results. These findings require prospective multicenter external validation and clinical implementation studies before broader adoption in routine practice.