The purple pen versus the purple bag.

Abstract

Objective: To highlight successful treatment of a symptomatic catheter associated urinary tract infection (CA-UTI), with an unusual 'purple bag' as the presenting complaint. Clinical features: A 78-year-old male attending a routine vascular clinic appointment for monitoring of an abdominal aortic aneurysm reported that his long-term urethral catheter drainage bag was bright purple. Other relevant medical history included mild chronic renal impairment due to a large right-sided inguinoscrotal hernia. Literature review: 'Purple bag syndrome' is an uncommon occurrence in catheterised patients, where urine in the drainage bag turns purple, due to colonisation with certain bacterial species (commonly Providencia, Proteus mirabilis, Klebsiella pneumonia and Citrobacter). Through a series of bacterial biochemical reactions, tryptophan metabolism results in production of pigments indirubin (red) and indigo (blue), creating purple discolouration. Risk factors include female gender, increased dietary tryptophan, alkaline urine, constipation, high urinary bacteria load and renal failure. Pharmacist interventions, case progress and outcomes: Advice was sought from the Infectious Diseases Pharmacist, who requested additional information from the surgical team prior to recommending a specific treatment, to confirm additional symptoms consistent with a CA-UTI. In this instance the patient described new onset, vague lower back pain. As the 'purple bag' indicates bacteriuria only, it is essential to ensure that additional symptoms compatible with infection are present, as asymptomatic bacteriuria should not be treated with antibiotics, even if visually striking. Empirical treatment with trimethoprim/sulfamethoxazole was commenced, based on knowledge of the organisms commonly implicated, and local antibiogram data. Subsequent urine culture reported Proteus mirabilis, sensitive to amoxicillin, cefalexin and trimethoprim, with a urinary pH of 9. The catheter was replaced one week later using a guide-wire, at which time urine colour has returned to normal. Conclusion: This case demonstrates successful antimicrobial treatment of 'purple bag syndrome' in a symptomatic CA-UTI.