Because a newly available point-of-care test may have real interest especially for children in the Emergency Department (ED) setting, by limiting painful and stressful venipunctures and decreasing the length of stay in the ED, the investigators hypothesize that integrating this new capillary Procalcitonin (PCT) rapid test in the DIAFEVER CPR (Clinical Prediction Rules) could represent a highly valuable diagnostic tool to identify a group with low Invasive Bacterial Infection (IBI) risk and could limit unnecessary exams and antibiotic prescriptions. The aim of this present study is to demonstrate the impact of this new PCT rapid-test-based CPR on antibiotic prescription rate in young children with Fever Without Source (FWS) presenting to the ED and on morbidity and mortality

This prospective multicentric randomized study will include 5000 febrile children aged six days to three years, diagnosed with fever without source, in 26 participating French and Swiss emergency departments, during a 36-month period.

During one period, all children will receive usual care. In a second period, the DIAFEVER algorithm will be applied in half of the clusters, and in the remaining clusters, children will still receive usual care.

Then in the last period of one year, all centers will apply the new PCT-based algorithm.

At day 15 after the first consultation, data concerning death, intensive care unit admission, disease-specific complications, diagnosis of bacterial infections and proportion of antibiotic treatments will be assessed by questioning parents by use of an online electronic case report form or a phone call. The endpoints will be compared between the two groups by using a mixed logistic regression model adjusted on clustering of participants within centers and period within centers.

To perform complementary studies, a biocollection will be proposed to parents when blood tests will be indicated.

Inclusion Criteria:

• Febrile children aged 6 days to <36 months old presenting to an ED at their initial visit with an acute illness for a maximum of 8 days and diagnosed with a FWS defined as body temperature (measured at home or the ED) > 38°C and a physical examination by a physician without source
• Oral non-opposition will be requested from one of the parents or caregivers of the patient.
• No current antibiotic treatment or within the 48 hours before the ED presentation.
• Parental affiliation with an appropriate health insurance system
• Parents speaking French

Exclusion Criteria:

• A clear source of fever identified after a careful inspection of medical history and a physical examination
• No fever on consultation or previously subjectively assessed by parents without use of a thermometer
• Refusal of the parents to participate
• Child ≥ 36 months or < 6 days old (ie, early-onset neonatal infection)
• Ongoing ABT treatment or within the 48 hours before ED presentation
• Children with FWS who revisited the ED after their initial visit
• Participation with another interventional study involving human subjects or being in the exclusion period at the end of a previous study involving human subjects