The decision to start IFX is the sole decision of the treating physician based on the patient's immediate need. Eligible patients are those who are planned to start IFX. All patients will undergo clinical and laboratory evaluation for IFX eligibility (PPD, infectious serology). If the tests have already done in the last 3 months, we will use these data, there is no need to repeat. Patients must have a negative stool culture, stool for parasites and clostridium difficile toxin test performed over the last week in order to be eligible. The screening visit may be performed concomitantly with the enrolment visit if all inclusion and exclusion criteria are met.