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Article History

Received: 17 March 2026

Accepted: 1 July 2026

First Online: 31 July 2026

Declarations

Ethics approval and consent to participate: The study protocol conforms to the ethical guidelines of the 1975 Declaration of Helsinki (6th version, 2008). The study protocol was approved by the Institutional Review Board of Meyer Children’s Hospital IRCCS.

Consent for publication: Written informed consent for data publication was obtained from the parents of enrolled children.

Competing interests: The authors have no relevant financial or non-financial interests to disclose.

FEBRIOUT study group: FEBRIle infant withOUT a source: Elena Altieri 1 , Lorenza Baroni 2 , Roberta Caiazzo 3 , Crescenzo Coppola 3 , Giulia Dal Canto 4 , Margherita Del Bene 5 , Giada Di Pietro 6 , Federica Forlanini 7 , Chiara Gabrielli 8 , Luisa Giannone 9 , Ilaria Liguoro 10 , Giulia Lorenzetti 11 , Caterina Marabotto 12 , Carmela Mercogliano 13 , Sara Monaco 14 , Cristina Moracas 5 , Marco Antonio Motisi 15 , Paola Musso 16 , Francesco Nunziata 13 , Victoria Rinaldi 8 , Alessia Sallemi 7 , Marco Sarno 17 , Agnese Tamborino 18 , Marco Zaramella 19 1 ASST Grande Ospedale Metropolitano Niguarda, Milan, Italy 2 Neonatology and Neonatal Intensive Care Unit, ASMN Reggio Emilia, Reggio Emilia, Italy 3 Pediatric Infectious Disease Unit, Luigi Sacco Hospital, University of Milan, Milan, Italy 4 Pediatric Unit, Imola Hospital, Imola, Italy 5 Pediatric Infectious Disease Unit, Department of Maternal and Child health, University Hospital “Federico II”, Naples, Italy 6 Department of Pathophysiology and Transplantation, Pediatric Highly Intensive Care Unit, Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, University of Milan, Milan, Italy 7 Paediatric Department, Buzzi Children’s Hospital, Milan, Italy 8 Division of Pediatrics, Nuovo Ospedale San Giovanni Battista, Foligno; Ospedale Civile San Matteo degli Infermi, Spoleto, Italy 9 ASST Spedali Civili, Brescia, Italy 10 Division of Pediatrics, University Hospital of Udine, Udine, Italy 11 Infectious Diseases Unit, Bambino Gesù Children’s Hospital, IRCCS, Rome, Italy 12 Department of Pediatrics, Bambino Gesù Children’s Hospital, IRCCS, Palidoro, Rome, Italy 13 General Paediatrics and Immuno-Rheumatology Unit, National Specialty Hospital Santobono Pausilipon, Naples, Campania, Italy 14 Pediatric Unit, Fidenza Hospital, Local Health Authority, Parma, Italy 15 Pediatrics and Neonatology unit, Maternal-Infant Department, San Giuseppe Hospital, Empoli, Italy 16 Department of Pediatrics, SS. Annunziata Hospital, Savigliano (CN), Italy 17 Chronic Diseases, Hepatology and Nutrition Unit, Santobono-Pausilipon Children’s Hospital, Naples, Italy 18 Paediatric Infectious Disease Unit, Meyer Children’s Hospital IRCCS, Florence, Italy 19 Pediatrics and Neonatology unit, Ospedale Unico della Versilia, Lido di Camaiore (LU), Italy