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Capnocytophaga canimorsus感染症は犬・猫による咬掻創感染症の一つであり，多くが敗血症を呈し死亡率約30%に達する。本邦での報告は大変稀であったが，近年報告数が増えつつある。症例は70歳の女性。来院2週間前，飼い犬に右手指を咬まれて数日で自然治癒した。来院前日より発熱・下痢が出現，来院当日12時頃に不穏状態となったため当院へ救急搬送された。血液検査で炎症反応上昇と凝固能障害，およびCTで腸管浮腫と脾臓低形成以外の有意所見を認めず，明らかな熱源は同定できなかった。当初は感染性腸炎による敗血症・DICと診断し，抗菌薬投与含め全身管理を開始した。第1病日より人工呼吸管理を必要としたが，全身状態は経時的に軽快し，第33病日に自宅退院となった。血液培養でグラム陰性桿菌を検出し，犬咬創歴が入院後判明したことから，下痢症状とあわせてC. canimorsusを疑った。第18病日に遺伝子検査で菌が同定され，C. canimorsus感染症による敗血症性DICと確定診断した。本症例は犬咬創後2週間経過しており，受傷痕もなく早期診断は困難であったが，動物咬創歴が診断の鍵となった。感染源不明の敗血症・DICの原因として，C. canimorsus感染症は鑑別に挙げる必要がある。 Capnocytophaga canimorsusinfection is a zoonosis caused by dog or cat bites, and sepsis caused by C. canimorsusis associated with up to 30% mortality. Although currently few, case reports of C. canimorsusare increasing in Japan. A 70–year–old woman arrived at our hospital with fever, diarrhea and delirium. She had been bitten on her finger by her dog 14 days earlier. Sepsis and disseminated intravascular coagulation were diagnosed by blood tests. CT examination revealed a hypoplastic spleen. Because no focus of infection was identified, infectious enteritis was initially suspected. After hospital admission, C. canimorsusinfection was suspected based on the isolation of Gram–negative rods from blood cultures and her medical history. She was intubated on hospital day 1, but her condition improved gradually such that she was extubated on day 12 and discharged on day 33. Finally, C. canimorsuswas detected by blood culture. Late onset after dog bite and absence of bite wound made it difficult to diagnose infection earlier. The key to suspicion was her dog bite history. In patients with sepsis of unknown origin, C. canimorsusinfection should be considered.