In recent decades, different tests have been recommended by guidelines in the management of first febrile urinary tract infection (fUTI) in children, including kidney ultrasound (KUS), cystography (VCUG) and renal scintigraphy in order to exclude underlying kidney anomalies. The majority of guidelines, continue to recommend a routine KUS for all children at the first fUTI. On the other hand, as this approach is not based on robust evidence, other guidelines suggest that KUS should only be performed on selected patients according to specific risks. Despite being a non-invasive and radiation-free method, KUS tests negative in 83% of cases of fUTIs and possesses low specificity for low grade vesico-ureteral reflux (VUR). Since VUR is the most commonly associated renal malformation with UTI, it is evident that all the guidelines focus on the research of VUR, especially in times when antenatal ultrasound allows to screen for major congenital anomalies of kidney and urinary tract (CAKUT). However, VUR-associated nephropathy appears to be related to primary dysplastic damage rather than to be secondary to the reflux itself and not preventable from antibiotic prophylaxis in terms of recurrence and of kidney scar. To reduce the number of normal VCUGs performed, recent evidence regarding VUR suggests that the presence of pathogens different from E. coli and UTI recurrence may help to identify children who necessitate further investigations. A preliminary retrospective monocentric study enrolling all patients aged 2 to 36 months diagnosed with first fUTI who subsequently underwent US evaluation of the kidneys and urinary tract, found that atypical germ and recurrence of UTI exhibits a 85% sensitivity to detect pathological ultrasound. The aim of this multicentric study is to prospectively evaluate the diagnostic accuracy of the presence of atypical germ combined with the recurrence of UTI in predicting the positivity of KUS in children aged 2 months to 3 years old with first episode of fUTI

Inclusion Criteria:

- Patient with first episode of fUTI that subsequently do KUS.

Exclusion Criteria:

• patients with previous episodes of UTIs
• patients on antibiotic prophylaxis
• previous finding of malformative uropathies or cystic disease
• prenatal diagnosis of CAKUT with the following parameters: Presence of oligohydramnios, alterations in renal number, location and echo structure, bladder alteration, dilations of the renal pelvis and ureters

Children aged 2 months to 3 years with the first episode of urinary tract infection