Study Design and Setting: Prospective observational study of 1,750 febrile children aged !16 years, visiting the emergency department of a university hospital; of them 13% (n5222) had SBI. Common age-specific thresholds of heart and respiratory rates were used to define tachycardia and tachypnea. We compared seven strategies to handle vital signs as predictors of SBI (dichotomized or continuously in various ways).