Pro-RAPID

Prior treatment

• Patients with the following characteristics will be excluded: - Established monogenetic IBD - Diagnosis with UC or IBD-U, ulcerative colitis like - Severe comorbidity (not related to IBD) - Immediate need for surgery (i.e., symptomatic stenosis or stricture in the bowel) - Severe infection such as sepsis or opportunistic infections, positive tuberculin test or a chest radiograph consistent with tuberculosis or malignancy - Pregnancy, suspected or definitive - Treatment with anti-TNF or other biological drugs in the past - Start of corticosteroids or mesalazine less than 2 weeks prior to first IFX infusion - Start of Exclusive Enteral Nutrition less than 2 week prior to first IFX infusion

• Anti-TNF-α naïve children (age 1-15 years) with CD or IBD-U and an indication to start IFX treatment will be eligible for inclusion after a diagnosis of CD is made based on the Porto criteria [10]. Indications of starting IFX treatment as per ECCO-ESPGHAN guidelines [9] include non-response after induction with exclusive enteral nutrition or steroids, non-response to immunomodulators, severe growth delay, extensive disease and/or structuring or penetrating disease, with or without perianal disease. Evaluation of the indication to start IFX is performed at the discretion of the attending physician.