GEODESIC is a prospective descriptive cohort investigation that will examine the generalizability of the novel host gene expression biomarkers, SeptiCyteTM LAB, SeptiCyteTM VIRUS, SeptiCyteTM BACT, and SeptiCyteTM TRIAGE (collectively 18 genes or SeptiCyteTM LVBT) and SeptiCyteTM RAPID, for differentiating children with bacterial sepsis, versus severe viral illness, versus non-infectious related systemic inflammatory response syndrome.

Specific Aim 1. Validate the robustness of the SeptiCyteTM LVBT gene expression signatures for providing clear discrimination between critically ill children with bacterial sepsis versus severe viral illness versus infection-negative systemic inflammation (INSI) secondary to a variety of etiologies.

Approach: We will expand our previous Genotypes And Phenotypes in Pediatric SIRS and Sepsis (GAPPSS) INSI cohort to children with recent trauma, thermal burns, anoxic-ischemic reperfusion events, exposure to cardiopulmonary bypass, extracorporeal life support, or dialytic therapy, CAR-T cell therapy, and various rheumatologic diagnoses. e we will recruit children with bacterial and viral infection who demonstrate a spectrum of illness severity and organ dysfunction. This specific aim will demonstrate the generalizability of SeptiCyteTM LVBT among critically children with life-threatening infectious disease or INSI.

Specific Aim 2. Determine if SeptiCyteTM LVBT gene expression signatures trend towards resolution of previously induced or suppressed gene expression states as critical illness resolves.

Approach: We will obtain paired blood samples for SeptiCyteTM LVBT gene expression, the first around the time of intensive care unit (ICU) admission (critically ill) and the second at ICU discharge approximately 48 hours later (transition to acute care). Resolution of critical illness will be quantified by serial daily measures of composite organ dysfunction.

Specific Aim 3. Ascertain that performance of SeptiCyteTM RAPID utilizing a point of care device at Seattle Children's will be equivalent to centralized assessment using SeptiCyteTM LAB.

Approach: Blood samples will be processed on site (Seattle Children's) for SeptiCyte RAPID testing. SeptiCyteTM RAPID is the result of the translation of the SeptiCyteTM LAB test to the cartridge-based Biocartis Idylla™ platform.

Inclusion Criteria:

INSI Cohort

• Admitted to the PICU
• New severe trauma OR
• New thermal burns OR
• Rheumatologic diagnoses OR
• Post-initiation (or circuit change) of extracorporeal life support OR
• Post anoxic-ischemic-reperfusion insults OR
• Infants undergoing cardiac surgery with cardiopulmonary bypass OR
• CAR-T cell therapy
• Parents speak English or Spanish AND
• Not previously enrolled in the GEODESIC investigation

Pediatric Bacterial Sepsis Cohort

• Admitted to the PICU
• Parents speak English or Spanish AND
• Exhibit SIRS criteria including at least fever/hypothermia or leukocytosis/leukopenia or left shift on the leukocyte differential AND
• Strongly suspected or documented source of bacterial infection per primary care team
• Not previously enrolled in the GEODESIC investigation

Pediatric Bacterial Sepsis Cohort

• Admitted to the PICU
• Parents speak English or Spanish AND
• Positive PCR or culture verifying a viral infection
• Not previously enrolled in the GEODESIC investigation

Exclusion Criteria:

• Not expected to survive the PICU stay
• Child has 'ward of the state' status

Critically ill children with systemic inflammatory response secondary to bacterial or viral sepsis or non-infectious SIRS