Study Investigating Tailored Treatment With Infliximab for Active Crohn's Disease

Inclusion Criteria: * Age \> 18 years * Active CD (CDAI\>220) and signs of active inflammation as evidenced by elevated serum hsCRP levels (\>5 mg/L) and/or elevated fecal calprotectin levels (\>250 µg/g) and endoscopically visible ulcers. * Patients must be naïve to biologics with indication for starting anti-TNF therapy in accordance with national reimbursement criteria. * Patients must be naïve to thiopurines or have failed therapy with thiopurines (in which case AZA will be continued). * Ongoing steroids are allowed if at stable dose for at least 2 weeks and at a maximum of prednisone 40 mg/d or budesonide 9 mg/day. * Patients who consent to receiving Infliximab 5 mg/kg at week 0, 2 and 6 and further on every 8 weeks in conjunction with azathioprine (2,5 mg/kg/day). Patients who develop AZA intolerance during the trial are continued in the trial without AZA (ie IFX monotherapy). Exclusion Criteria: * Absence of endoscopically visible ulcers * Prior exposure to infliximab (other biologics allowed) * Ongoing steroid therapy at doses \> 40 mg/d prednisolone equivalent * Previous intolerance to azathioprine leading to drug discontinuation * Ongoing infections * Positive tuberculosis screen per local guidelines * Serious other diseases including cancer in the 5 years prior to inclusion excluding non-melanoma skin cancer * Indication for immediate surgery * Pregnant or breast-feeding woman. * Positive fecal culture for Salmonella, Shigella, Yersinia and Campylobacter and/or presence of Clostridium difficile B toxin in the stools * Active tuberculosis * Untreated latent tuberculosis (see national recommendations. Appendix 2). * Non-compliant subjects. * Participation in another therapeutic study.