Streptococcus pyogenes aortic aneurysm infection: forgotten but not gone
A 60 year old man had a past history of smoking, non-alcoholic steatohepatitis and a left ileofemoral bypass with a Polyethylene Terephthalate (Dacron) graft 7 years earlier. His only regular medication was esomeprazole. He became unwell during a trip to the United Kingdom, with sore throat, fevers and sweats. On return to Australia, fever and night sweats persisted, and he had 8 kg weight loss. Four weeks later he presented with back pain, an abdominal computed tomography (CT) scan revealed a para-aortic mass (), and he was referred to our emergency department for further management. On examination he was afebrile, heart rate 60 beats/min, normotensive with a pulsatile non-tender abdominal mass. White cell count (WCC) was 13.9×109/L and C-reactive protein (CRP) 207 mg/L. As he was clinically stable, empiric antibiotic therapy was withheld. Multiple blood cultures were obtained and a CT-guided biopsy of the periaortic mass was performed. Following the biopsy, he developed fever (40°C) and rigors, and intravenous ceftriaxone 2 g every 24 hours, vancomycin 1.5 g every 12 hours and metronidazole 500 mg every 12 hours were commenced. Blood cultures and biopsy specimens revealed pure growth of Streptococcus pyogenes, later confirmed as emm type 44. Antimicrobial therapy was modified to iv benzylpenicillin 2.4 g q4h alone. Transoesophageal echocardiography revealed no evidence of endocarditis. He was progressing well until day 7 when he developed worsening abdominal pain. Repeat abdominal CT scan revealed a contained rupture of the aneurysm. He underwent urgent endovascular aortic aneurysm stent graft repair. Fever resolved in 72 hours, and inflammatory markers reduced (Day 4: WCC 15.3×109/L and CRP 430 mg/L; Day 13 WCC 6.8×109/L and CRP 66 mg/L). He was discharged on day 15 and continuous infusion intravenous benzylpenicillin was continued via an outpatient antimicrobial therapy program, with a plan for 6 weeks therapy followed by lifelong oral amoxicillin.\nHowever he had ongoing weight loss, anorexia, his inflammatory markers failed to normalise. On day 53, he underwent graft explantation and axillo-bifemoral bypass. This was complicated by graft occlusion requiring therapeutic anticoagulation, and subsequent intra-abdominal haemorrhage. This ultimately resulted in irreversible ischemia of his left lower limb requiring below knee amputation. Culture of the explanted graft revealed Klebsiella oxytoca, Enterococcus faecalis, and methicillin-sensitive Staphylococcus capitus and Staphylococcus epidermidis, but Streptococcus pyogenes was not reisolated. Repeat CT imaging revealed no source of infection, and there was no evidence of intestinal pathology at the time of laparotomy. He was treated with intravenous piperacillin/tazobactam 4.5 g every 8 hours for a further 6 weeks, followed by oral amoxicillin/clavulanate, with a plan for lifelong antimicrobial therapy. On review 4 months after the initial presentation, he was recovering uneventfully and inflammatory markers had normalised.