Fig. 1. Multivariable modeling architecture and causal variable selection framework. Overview of candidate predictor pool (n = 908), prespecified inclusion criteria (univariate P < 0.10, age and sex adjustment, VIF < 2.0), strict causal exclusions (eliminating circular ICU stay, total hospital stay, and collinear composite CCI scores), and final logistic model formulation targeting severe Clostridioides difficile infection (CDI).