This is a retrospective, blinded, external validation study of a novel in-vitro diagnostic (IVD) assay that will include samples that were previously collected from febrile pediatric patients. The investigated assay measures the levels of a few host-related, blood-based, bio-markers that will be integrated into a single score. Based on this score, each patient will be classified into one of three categories: (i) bacterial immune response, (ii) viral immune response, and (iii) marginal immune response. The assay prediction and the patient diagnosis will than be unveiled and compared to determine their level of concordance.