Purpura fulminans associated with <i>Capnocytophaga canimorsus</i> infection

Abstract

A previously well 49-year-old woman presented with a few days of flu-like symptoms. She was hypotensive and pyrexial, with a wound on her left thumb due to a 5-day-old dog bite. Laboratory investigations showed leucopenia and thrombocytopenia (Hb 13·1 g/dl, platelet count 23 × 109/l, white cell count 1·7 × 109/l) and a mild coagulopathy [prothrombin time – 24 s (normal range, NR: 10–13 s), activated partial thromboplastin time – 58 s (NR: 26–36 s), fibrinogen concentration 1·82 g/l (NR: 1·5–4·5 g/l)]. She was commenced on antibiotics and intravenous fluids and given fresh-frozen plasma. Shortly after admission her platelet count was 14 × 109/l, Hb 8·9 g/dl and a blood film showed features of a microangiopathic haemolytic anaemia. No intracellular organisms were seen. Lactate dehydrogenase was elevated at 1053 U/l. Although the coagulopathy rapidly resolved, she subsequently developed renal failure, requiring haemodialysis, and progressive digital ischaemia, consistent with purpura fulminans (top images and bottom left). Plasma exchange was commenced. A gram-negative bacillus was detected in blood cultures. Over the next 5 d she improved, the thrombotic angiopathy resolved and plasma exchange was discontinued. She was discharged 2 weeks later off dialysis and remains well, but has required plastic surgery to her left hand. The organism was identified as Capnocytophaga canimorsus, a slow-growing commensal found in the mouths of cats and dogs, sensitive to most broad-spectrum antibiotics, except aminoglycosides. Capnocytophaga sepsis has a mortality of approximately 30% and is more common in immunocompromised patients, especially those with a history of splenectomy or alcohol abuse. The bottom right image shows a blood film from a second patient who presented with septic shock and disseminated intravascular coagulation from Capnocytophaga canimorsus. Organisms were readily identifiable. She unfortunately died 4 d after admission. These cases highlight the importance of early antibiotic treatment for even trivial animal bites. The index case also displayed the potential use of plasma exchange in cases of severe sepsis associated with purpura fulminans.