Case Presentation: A 90 year old Caucasian female with history of complicated diverticulitis s/p partial colectomy and Waldenstrom’s Macroglobulinemia (last treatment with Cyclophosphamide and Dexamethasone 1 week prior to presentation) was admitted with 2 day history of crampy lower abdominal pain, bloody streaked diarrhea, vomiting, and subjective chills. Physical examination elicited tachycardia and diffuse abdominal tenderness without guarding or rebound tenderness. Laboratory results were significant for leukocytosis at 14.5*10³/μL (normal range 4.3-10.8) and an elevated lactate at 4.9 mmol/L (normal < 2). The patient's CT scan of abdomen/pelvis showed long segment colitis in the transverse, descending, and sigmoid colon. While awaiting blood cultures, her sepsis was empirically treated with intravenous Vancomycin and Piperacillin-Tazobactam. Clostridium difficile toxin PCR was positive for which oral Vancomycin was started. Blood cultures initially showed gram-positive bacilli growing at 19 hours assumed to be C. difficile, but eventually revealed as Clostridium innocuum. Antibiotics were changed to oral Metronidazole and oral Vancomycin with continued improvement in her condition.

Discussion: Normally a harmless intestinal commensal, Clostridium innocuum gained its name due to its once-thought innocuous nature and lack of toxin production. However, it has since been isolated in various fatal infections such as endocarditis, osteomyelitis, and bacteremia. To our knowledge, there have been only 13 cases of Clostridium innocuum bacteremia reported, particularly in patients experiencing various immunocompromised states such as organ transplant, acquired immunodeficiency syndrome, leukemia, and diabetes. There have been no other reported cases in patients with Waldenstrom’s macroglobulinemia. Some reports have suggested that there is a statistically significant increase in mortality with C. innocuum bacteremia compared to other Clostridial species. One case report found Vancomycin-resistant C. innocuum bacteremia after treatment of C. difficile with oral Vancomycin, however our patient had concurrent presentation of both of these infections. Despite variable efficacy of oral Vancomycin, oral Metronidazole has shown to be an effective treatment for this infection likely due to its high bioavailability of 98.9% allowing for greater concentrations in the blood. This may be in combination with a gene that could predispose C. innocuum with resistance against the D-Ala-D-Ala inhibition of Vancomycin.

Conclusions: Despite C. innocuum’s role as a normal part of the gut flora, it can become dangerous in an immunocompromised patient. Early diagnosis and effective treatment of this rare infection with Metronidazole can improve patient outcomes. It should be recognized as an emerging and invasive infection in immunocompromised hosts, especially in patients with a recent history of C. difficile diarrhea.

IMAGE 1: Colitis on CT Imaging

IMAGE 2: C. innocuum Microscopy (courtesy of Getty)