This is a prospective clinical validation study of a novel regulatory approved (CE-IVD) diagnostic assay called ImmunoXpert™ that will enroll 1222 pediatric patients. The study aims to externally validate the tool's diagnostic accuracy and estimate the potential improvement in health and economic outcomes following the usage of ImmunoXpert™. Additionally, statistical analysis will be performed to compare ImmunoXpert™ accuracy to current practice lab testing (e.g. WBC, CRP, and PCT) and clinical suspicion at time of requisition. Enrolled patients will be managed according to the current standard of care and per standard institutional procedures.

Inclusion Criteria:

• Legal guardian signs an informed consent
• Documented peak temperature ≥ 38°C (100.4°F)
• Symptom duration ≤ 7 days
• Clinical suspicion of RTI (OR) fever without a clear source after clinical examination

Exclusion Criteria:

• Another episode of febrile infection within the past 2 weeks
• Antibiotic treatment of over 48 hours
• Congenital immune deficiency (CID)
• A proven or suspected HIV, HBV, HCV infection
• Active malignancy
• Current treatment with immune-suppressive or immune-modulating therapies, including without limitations:
• Use of high dose steroids >1 mg/kg/day prednisone or equivalent in the past two weeks
• Monoclonal antibodies, anti-TNF agents
• Intravenous immunoglobulin (IVIG)
• Cyclosporine, Cyclophosphamide, Tacrolimus
• G/GM-CSF, Interferons
• Other severe illnesses that affect life expectancy and/or quality of life such as:
• Severe psychomotor retardation
• Post-transplant patients
• Severe congential metabolic disorder

Eligible subjects from both genders that present to the ED due to suspected RTI, or FWS. Each of these patients falls into one of the following categories:

1. Patients with an acute bacterial infection
2. Patients with an acute viral infection
3. Patients with an acute co-infection (bacterial and viral)
4. Patients with an undetermined disease etiology