Title

‘A Deadly Dog Bite’

Authors

Martin Baxter, MBBS, Christian Seedarnee, MBBS, Zola Nlandu, MBBS.

Introduction

Capnocytophaga species are rare but significant bacterial causes of morbidity and mortality following dog bites, with an estimated case fatality rate of up to 30%. This fusiform gram negative rod is a fastidious, slow-growing, anaerobe and while early blood culture identification may not be possible, clinicians must keep a high index of suspicion for this infection in at-risk individuals.

Case Presentation

We present a case of a 44-year old male with a history of alcohol dependence, presenting with fever and malaise of two days duration following an unprovoked hand bite from a family dog. On admission he had a temperature of 100.7 Fahrenheit, HR 114 bpm, BP 133/88 mmHg, RR 21/min, SpO2 91% on room air. Physical exam was significant for a 0.2 x 0.2cm puncture wound to the left hypothenar eminence with surrounding erythema and a diffuse purpuric rash noted to his chest, abdomen and legs. Biochemistry revealed a WBC of 2.90 x 10^3/µL, Hemoglobin 14.4g/dL, Platelet count 49 x 10^3/µL Creatinine 1.48 mg/dL, AST 110 U/L, ALT 105 U/L, TBili 1.1 mg/dL and Lactate 4.8 mmol/L. He was admitted for severe sepsis, left hand cellulitis, AKI, DIC and started on piperacillin-tazobactam and vancomycin. Rapid deterioration over the following 12 hours with worsening multi-organ failure led to intubation, blood product transfusions and transient vasopressors in the ICU. Infectious Diseases voiced concerns for Capnocytophaga species contributing to the clinical picture while awaiting blood culture results. Subsequently, the patient developed severe renal failure requiring dialysis, NSTEMI and left upper limb myonecrosis with compartment syndrome requiring transhumeral amputation. Blood cultures initially identified Klebsiella species, however due to ongoing clinical suspicion that Klebsiella was an unlikely cause of the severe presentation, a subsequent anaerobic subculture identified Capnocytophaga canimorsus after 7 days. He developed bilateral acute lower limb ischemia requiring amputation secondary to thrombotic DIC. Due to a rapidly falling platelet count and concern for bleeding risk he was not initially started on systemic anti-coagulation until later in his presentation. Questionable skin viability when planning bilateral lower limb amputation prompted transfer to a burn center. He remained on piperacillin-tazobactam at the time of transfer. He subsequently underwent bilateral above knee and three right hand digit amputations, with debridement of his nose, lips, ears and maxilla due to gangrene. He was placed on thrice weekly hemodialysis.

Discussion

Capnocytophaga species are part of human and canine oral flora, of which C.canimorsus is responsible for most severe infections. The species is known for causing fulminant sepsis, especially in immunosuppressed patients, including those with heavy alcohol use as in our patient. Diagnosis is established by blood culture however due to its fastidiousness, identification can take up to 14 days. Thus, there should be a high index of clinical suspicion of Capnocytophaga infection following a dog bite in a patient presenting with septicemia, purpura fulminans, DIC with known risk factors, despite negative cultures early in the clinical course- especially given its high morbidity and mortality rate.

References

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