An 82-year-old Japanese man was admitted to our hospital because of a 3-day history of chills and abdominal and back pain. He was diagnosed with rheumatoid arthritis, for which he had been prescribed methotrexate 4 mg/week 2 years earlier. Additionally, he had a history of hypertension and angina pectoris. He had no history of tuberculosis, syphilis, or previous abdominal surgery. He denied having any digestive symptoms such as nausea, diarrhea, or melena. There was no evidence that he had a colonic diverticulum.
On admission, he was alert, his vital signs were blood pressure of 144/84 mmHg, heart rate of 115 beats/min, body temperature of 38.3 C, respiration rate of 16 breaths/min, and SpO2 of 96% with ambient air. His physical examination revealed pain and tenderness on his right lower abdominal quadrant, but no pulsatile masses.
Laboratory findings showed an elevated white blood cell count of 16,400/muL (neutrophils, 92%; lymphocytes, 2.1%) and C-reactive protein of 22.39 mg/dL. His serological tests for syphilis were negative. Enhanced computed tomography displayed an abdominal aortic aneurysm (Figure).
According to a clinical suspicion of a mycotic aneurysm, three sets of blood cultures were obtained on admission, followed by a series of blood cultures taken on 3 consecutive days. Ceftriaxone 2 g intravenously (IV) every 12 h and vancomycin 1 g IV every 24 h were immediately administered for coverage of Gram-positive cocci and Gram-negative bacilli, such as Salmonella spp. We consulted a cardiovascular surgeon who recommended medical therapy as the primary therapy, but with continuous monitoring. The six sets of blood cultures obtained from the patient were negative. Then, vancomycin was discontinued because it was less likely that the infection was caused by Gram-positive bacteria.
On the seventh hospitalization day, he developed a high-grade (40 C) fever. Abdominal ultrasound revealed acalculous cholecystitis. At that time, two additional sets of blood cultures were obtained, and ceftriaxone was replaced with cefepime 2 g IV every 12 h.
On the ninth hospitalization day, the abdominal aneurysm became enlarged and finally ruptured; therefore, urgent open debridement and in situ replacement were performed. There was no evidence indicating either intestinal or colonic comorbidity or any abnormal laparoscopic findings. No serious complications occurred during the surgery. The Gram stain of the necrotic tissue of the aortic wall revealed Gram-negative bacteria suspected to be an anaerobe; thus, piperacillin/tazobactam 4.5 g IV every 6 h and metronidazole 500 mg PO (per os) three times daily were administered according to the general antimicrobiogram findings. On the 11th hospitalization day, piperacillin/tazobactam was replaced by sulbactam/ampicillin 1.5 g IV every 6 h because B. fragilis was isolated from the tissue culture. The bacterial profile indicated that the strain was sensitive to sulbactam/ampicillin and metronidazole, but resistant to clindamycin. While sulbactam/ampicillin was discontinued on the 22nd hospitalization day because of a skin eruption, metronidazole was maintained as suppressive therapy. The patient was discharged after 32 days of hospitalization without any complications. Metronidazole was discontinued after 6 months of treatment because the patient complained of dizziness. The dizziness disappeared and the patient was free of infection relapse for 3 years after the cessation of metronidazole. He ultimately died from an unrelated case of pneumonia.