Ruling out diagnosis of acute febrile illness in the ED is usually done relying on history, physical examination, routine laboratory tests (complete blood count, CRP, pro-calcitonin, urine dipstick), cultures (blood, urine. CSF, stool, throat culture etc.), imaging studies (Chest X-ray, ultra-sonography etc.) and other tests (lumbar puncture, serology, PCR etc.). the study:" Validation of markers for diagnosing the source of infection in pediatric febrile patient" number 0071-10-HYMC ("curiosity" study, see appendix A) is a prospective trial started in 2010 set in Hillel-yaffe hospital in Hadera, Israel. In this study patients with up to seven days of febrile illness, are recruited from the ED or pediatric department, history is taken that includes the home given therapy, blood tests are taken for complete blood count (CBC), culture and C-reactive peptide (CRP), imaging examinations are taken according to each case, PCR and Serology tests are taken to discern between number of agents (appendix A) and the final diagnosis is decided by a panel of infectious diseases specialists.