Summary

Crohn's disease patients undergoing anti-tumor necrosis factor (anti-TNF) therapy such as infliximab face potential risks from opportunistic infections. We introduce the unique case of a 66-year-old male Crohn's patient, previously in remission, presenting with gastrointestinal symptoms following a trip to the Czechia. Despite concerns of reactivated tuberculosis due to infliximab, his biopsies showed the presence of Mycobacterium simiae (M. simiae). Despite this, anti-TNF therapy was continued and resulted in clinical improvement. This is a case report of M. simiae in intestinal biopsies of an immunocompromised Crohn's patient is a clinical challenge. The findings suggest the benign colonization of M. simiae potentially influences future treatment considerations in similar clinical scenarios.