3-day IV Antibiotic Treatment Versus 3-day IV Followed by 7-day Oral Antibiotic Treatment for AP in Children

Inclusion Criteria: * Age ≥ 1 month and \< 3 years * For children younger than 3 months, gestational age \> 34 WA * First episode of urinary tract infection * AP defined by temperature ≥ 38°C on day of diagnosis AND positive urinalysis (white cell counts ≥ 10\^4/mL) with a positive urine culture with one Gram- negative bacillus ≥ 104 UFC/mL. The child temperature will have to be measured with a thermometer according to the French national recommendations \[Health Insurance website (AMELI ;see: - https://www.ameli. fr/assure/sante/bons-gestes/soins/prendre-temperature); HAS (see: https://www.has-sante. fr/jcms/c\_2674284/fr/prise-en-charge-de-la-fievre-chez-l-enfant)\]. * Initial treatment by either ceftriaxone AND/OR amikacin * Outpatient or hospitalised Non-inclusion Criteria: * Urine collected by bag * Urine culture growing more than one dominant bacterium (cf section 6.2 of the protocol) * Catheter-associated acute pyelonephritis * Known congenital anomalies of the kidney and genitourinary tract (other than vesicoureteral reflux and pyelocaliceal dilatation \< 10 mm) * Previous surgery of the genitourinary tract (except circumcision in male children) * Abnormal renal function for age and weight (defined by a serum creatinine \>40µmol/L before 1 year and \>75µmol between 1 year et 3 years) * Known immunocompromising condition (e.g., HIV, primary immunodeficiency, sickle cell disease, use of chronic corticosteroids or other immunosuppressive agents) * Antibiotic prophylax…