A Rare Case of Multi-Organ Complications Due to Disseminated Citrobacter koseri Infection Originating From a Renal Abscess.

Citrobacter koseri is a gram-negative bacillus that can cause severe infections in immunocompromised individuals. While it is a rare urinary tract pathogen, its potential for dissemination and severe complications demands attention. We report the case of a 44-year-old male with poorly controlled type 2 diabetes mellitus who developed a disseminated C. koseri infection originating from a perirenal abscess. The infection extended locally, resulting in septic thrombosis of the left renal vein, and spread distantly, causing septic pulmonary embolism. The patient underwent multiple surgical interventions, including left nephrectomy and Hartmann's procedure, in addition to prolonged antimicrobial therapy. Despite persistent complications, including an intra-abdominal abscess with cutaneous fistulization and iatrogenic hydropneumothorax, a conservative management approach with antibiotic therapy ultimately led to clinical resolution. This case underscores the importance of early recognition, appropriate source control, and individualized antimicrobial strategies, particularly in patients with complex infections and multiple comorbidities.