Around 42,000 children suffer from severe sepsis each year in the US alone, resulting in significant morbidity, mortality and billion dollar expenditures in the US healthcare system. Sepsis recognition is a clinical challenge in children. Biomarkers are needed to tailor appropriate antimicrobial therapies and improve risk stratification. The goal of this study was to determine if gene expression profiles from peripheral blood were associated with pathogen type and sepsis severity in children treated for suspected sepsis. Overall design: Prospective cohort study in a tertiary pediatric emergency department. Participants were included if they were >56 days and <18 years of age, had suspected sepsis, and had not received broad spectrum antibiotics in the 4 hours prior to study eligibility. Control subjects (n=12) were patients in the same age range who had neither febrile illness nor treatment with antibiotics in the prior 14 days.