[Fever without a localizing source in infants]

In this chapter we will give an overview over the most frequent etiologies of fever in infants in Switzerland, propose an algorithm to evaluate this children, and we will end up with a discussion on the value of additional laboratory parameters. Fever in infants and small children is a leading cause for parents to seek medical attention. The vast majority has a self limiting viral infection, but all the same, all infants need to be thoroughly evaluated. After this process, the treating physician has to decide, which child needs to be specifically treated or cared for, either to avoid overtreatment nor overlooking a serious infection. Because of a broader immunization coverage against bacterial infections, the epidemiology of invasive bacterial disease is changing. Additional laboratory work up is sometimes necessary, but has it's limitations. The interpretation of lab values must taken into account the changing prevalence of serious bacterial infections. Newer parameters (e. g. Procalcitonin) are upcoming, of which the importance is still debatable. Fever causes in this age other than infectious diseases will be alluded.