S4014 The Diagnostic Significance of Clostridioides septicum Bacteremia in Detecting Underlying Gastrointestinal Malignancy

Introduction: Clostridium septicum is an uncommon but highly virulent, toxin-producing, gram-positive bacillus strongly associated with underlying malignancies, particularly colorectal cancer. Detection of this bacteria often signals the need for further evaluation. We report a case of C. septicum bacteremia in a patient with diabetes, leading to the diagnosis of previously undetected colonic adenocarcinoma. Case Description/Methods: A 59-year-old man presented with hyperglycemia (home glucose 570 mg/dL) and was admitted for diabetic ketoacidosis (DKA). Past medical history included type 2 diabetes mellitus, chronic hepatitis B with cirrhosis, and longstanding iron deficiency anemia without prior gastrointestinal workup. On admission, his hemoglobin was 5.9 g/dL. He reported no signs of bleeding and had never undergone prior colorectal cancer screening. During a blood transfusion, the patient became febrile, tachycardic, and hypotensive. One of 2 blood cultures drawn grew Clostridium septicum. Broad-spectrum antibiotics were initially started but discontinued early due to clinical improvement and low suspicion for true infection. Given the chronic anemia and positive culture, a colonoscopy was performed, revealing a large, ulcerated mass at the hepatic flexure. Biopsy confirmed the diagnosis of colonic adenocarcinoma. Imaging suggested possible peritoneal and pulmonary metastases, but biopsies were negative. The patient was discharged with oncology follow-up with plans for neoadjuvant chemotherapy. Discussion: Although uncommon, C. septicum bacteremia carries a high mortality rate and has a well-documented association with colorectal malignancy, particularly in diabetic patients. The bacterium thrives in hypoxic, acidic environments like those created by tumors, enabling mucosal translocation and systemic infection. Diabetic immunosuppression may increase vulnerability. Our patient's lack of overt infection symptoms led to early cessation of antibiotics. However, the positive culture, combined with unexplained anemia, prompted timely colonoscopy and cancer diagnosis. This case highlights the need for high clinical suspicion and early gastrointestinal evaluation when C. septicum is identified, even in clinically stable patients. C. septicum bacteremia, even from a single blood culture, should prompt urgent investigation for occult gastrointestinal malignancy in order to prevent delayed diagnosis of potentially life-threatening malignancies and to optimize patient outcomes.