When the Urine Turns Purple: Not Always a Urinary Tract Infection.

Purple urine bag syndrome (PUBS) is an uncommon but distinctive phenomenon characterized by violet discoloration of the urinary collection system. It occurs mainly in elderly, debilitated, and chronically catheterized patients, and although alarming, it is usually benign. We report the case of an 89-year-old woman with end-stage renal disease on hemodialysis and long-term catheterization who developed purple discoloration of the urine bag during hospitalization for influenza A. She remained asymptomatic, and the discoloration resolved after catheter replacement and optimization of bowel care without antibiotic therapy. PUBS results from bacterial metabolism of tryptophan into indigo and indirubin pigments that adhere to catheter surfaces, a process favored by constipation and chronic colonization. Recognition of this mechanism is crucial to distinguish PUBS from urinary tract infection and to prevent unnecessary antibiotic use. This case underscores the importance of clinical awareness and appropriate catheter management to ensure safe, evidence-based care in chronically catheterized patients.