Neonates (less than or equal to 28 days of age) and young infants (29-60 days of age) with fever account for a significant number of emergency department (ED) visits. At this age, there is an increased risk of serious bacterial infection (SBI) in urine, blood or the central nervous system. Most of these infants have self-limited viral illnesses, however up to 10-13% of febrile young infants have SBI (of which greater than 90% are urinary tract infections (UTIs). Clinical examination can be unreliable in determining the source or severity of infection. The difficulty lies in differentiating the infant with SBI from those without, while minimizing the risks of investigating and/or treating a febrile infant with no SBI. Additionally, young febrile infants are at risk of poor outcomes if SBI is not diagnosed and treated promptly.