Case Presentation: An 87-year-old male with a history of atrial fibrillation, a myeloproliferative disorder, and recently diagnosed cirrhosis presented with shortness of breath. He reported three weeks of progressive shortness of breath and weight gain, and on the night prior to admission, he developed fevers and chills. In the ED, he was febrile to 101.6 with a HR of 109. Exam was notable for an irregularly irregular heart rhythm, lungs with diffuse coarse rhonchi and decreased breath sounds at the right lung base, tense abdominal distension and 3+ pitting edema of bilateral lower extremities. Initial labs demonstrated WBC of 6.4 with 16% bands, BUN/Cr of 56/1.75 (baseline creatinine 1.2), and lactate of 2.8. PT and INR were 18.8 and 1.6, respectively. Two sets of blood cultures were sent, and empiric antibiotics were started. CT demonstrated a large right pleural effusion, ascites and splenomegaly.
He underwent a paracentesis and a thoracentesis. The paracentesis demonstrated SBP with gram negative rods on gram stain. The thoracentesis revealed an exudative pleural effusion without growth on gram stain or culture. One of two blood cultures grew Citrobacter braakii resistant to amoxicillin and cefazolin, and the patient’s antibiotics were transitioned to ertapenem. Subsequent blood cultures did not demonstrate growth. The patient had a protracted hospital course due to infection-induced pancytopenia and afib with RVR. After clinical stabilization, the patient and his family elected to pursue hospice in the setting of functional decline.

Discussion: The Citrobacter genus is a group of gram-negative bacilli part of the Enterobacteriaceae family. In addition to colonizing the intestinal tract, Citrobacter species have been shown to cause infections of the urinary tract, abdomen, skin and soft tissue, respiratory tract, CNS, and endovascular system. Although rare, C. braakii has been identified as a pathogenic organism.

Twelve cases of C. braakii have been described with ten of the twelve cases presenting with bacteremia. The remaining cases presented with peritonitis and a periungual abscess. Most patients had at least one primary underlying condition placing them at risk for opportunistic infections, and the most common source of the bacteremia was found to be intra-abdominal. Our patient had multiple comorbidities, which put him at risk for infection including cirrhosis and underlying malignancy.

Although C. braakii infections are uncommon, this may be due in part to the fact that it was only identified in 1993 and previous biochemical testing has been shown to inaccurately identify C. braakii as other Citrobacter species.

Conclusions: C. braakii is a gram-negative bacillus that causes opportunistic infections. Although currently rare, it is important for hospitalists to be aware of this organism especially in the setting of improvements in biochemical testing.