Necrotizing Fasciitis in an Immunocompromised Elderly Woman

1Department of Medicine; 2Institute for Infectious Diseases Research, Faculty of Health Sciences, McMaster University, Hamilton, Ontario Correspondence: Dr Jennie Johnstone, Department of Medicine, McMaster University, 3200 MDCL, 1280 Main Street West, Hamilton, Ontario L8S 4L8. Telephone 905-525-9140 ext 22726, fax 905-389-5822, e-mail johnsj48@mcmaster.ca Case Presentation An 85-year-old woman presented to hospital with a rapidly progressing erythema of the lower left leg. The patient was well until several hours before admission when she noted a small area of painful erythema on her left shin that progressed over 2 h to involve the entire leg below the knee. There had been no erythema noted earlier that day when her daughter bathed her. Her medical history was significant for hypertension, congestive heart failure, remote left total knee arthroplasty and a recent diagnosis of temporal arteritis for which 40 mg of prednisone daily was perscribed. She had no recent travel history and no sick contacts. On presentation, the patient appeared well, was not in distress and was hemodynamically stable with a heart rate of 80 beats/min, blood pressure of 120/60 mmHg and a temperature of 36.7°C. Her physical examination was remarkable for erythema over the anterior lower left leg, extending around the calf. There were no bullae. Although the leg was tender to palpation, the pain was not out of proportion with the area of erythema. There was no crepitus, and no ulcers or ports of entry were apparent. No regional lymphadenopathy was present. Examination of the left knee found no warmth, effusion or erythema, and there was complete and pain-free range of motion. The remainder of her physical examination was unremarkable. Initial investigations revealed a hemoglobin level of 146 g/L, a leukocyte count of 6.5×109/L, a platelet count of 146×109/L and a creatinine level of 51 μmol/L. Venous Doppler ultrasound of the left leg showed no evidence of deep vein thrombosis. Blood cultures were obtained before the patient was started on empirical intravenous antibiotic therapy with cefazolin (1 g every 8 h) and clindamycin (600 mg every 8 h). After 24 h of therapy, the erythema of the leg improved; however, severe foot pain developed in the absence of any erythema. She remained hemodynamically stable with a blood pressure of 140/80 mmHg and a heart rate of 80 beats/min and remained afebrile with a temperature of 36.5°C but had a notable drop in her leukocyte count to 1.8 ×109/L. Her creatine kinase level (26 U/L) was normal (normal <150 U/L). Due to the confusing clinical picture and in light of her immunocompromised status, antibiotic coverage was broadened by discontinuing cefazolin and starting piperacillin/tazobactam (4.5 g every 8 h). Approximately 36 h after admission, she acutely deteriorated, developing fever (37.9°C), hypotension (80/60 mmHg), a decreased level of consciousness, and worsened edema and erythema of the left leg extending above the knee with multiple small foci of necrosis. She required transfer to the intensive care unit for inotropic support. Vancomycin was added to the piperacillin/tazobactam and clindamycin, intravenous immunoglobulin was given, and an urgent orthopedic surgery consultation was obtained. A fascial biopsy was performed, which was sent for frozen section and culture. The biopsy was consistent with necrotizing fasciitis (NF) and the patient was taken to the operating room for urgent debridement, where an above-knee amputation was performed. Postoperatively, the patient experienced ongoing hypotension and a new area of erythema over the upper left thigh extending to the abdomen. The piperacillin/tazobactam was discontinued and meropenem was added. The next day, there was growth in the tissue culture from the fascial biopsy. What was the causative organism?

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