This is a prospective , double-blind , randomised , placebo-controlled , multicentre study of patients with luminal Crohn 's disease who have been treated with IFX for at least 1year and are in sustained complete clinical , biochemical and endoscopic remission ( ie , Crohn 's Disease Activity Index ( CDAI ) score < 150 , complete mucosal healing and biochemical markers of inflammation within the normal range ) .