Case Presentation: 64 year old male with history of PTSD, COPD, GERD, prostate cancer status post prostatectomy, hyperlipidemia and right total knee replacement presented after developing severe pain in his knees. Pain was associated with myalgia, malaise, arthralgia, anorexia, headache, chills, cough and weakness. Exposure history included travel to Seattle and recently working in a shed with rodent droppings. Patient owns 4 dogs and 2 cats. Vital signs at presentation were temperature 103.6⁰ F, blood pressure 89/51 mmHg, pulse 76 and respiration rate 28. Physical exam significant for patient in moderate distress, photophobia, nuchal rigidity, lungs with bibasilar crackles, knees and shoulder exquisitely painful to palpation without erythema, swelling or warmth. Labs significant for WBC 15.2 K/mm3 with 90% neutrophils, platelets 145 K/mm3 , sedimentation rate of 23 mm/hr and CRP 182 mg/L. Patient was admitted to the ICU in septic shock requiring vasopress ors and started on ceftriaxone and vancomycin. Antibiotics were broadened to piperacillin/tazobactam and vancomycin after meningitis was ruled out. He underwent surgical washout of the right knee. Synovial fluid analysis found total nucleated cell count 36700 #/mm3 with SEG 96%. Tests for Hantavirus, EBV/VCA, Parvovirus, CMV, Brucella, Rocky Mountain spotted fever, Coxsackie B1-6, HIV and acid fast organisms were all negative.
Both sets of blood cultures grew Capnocytophaga species. Synovial fluid cultures from the knee aspirate had negative growth, but PCR 16S sequencing was positive for Capnocytophagia canimorsus. Patient clinically improved on antibiotic therapy and was transitioned to amoxicillin/clavulanate to complete 8 weeks of therapy for prosthetic septic knee infection. Patient later reported that 2-4 weeks before becoming ill, he had open wounds on his right leg that his dogs kept licking.

Discussion: Capnocytophaga canimorsus is a slow growing, gram negative bacteria. It is found in the normal oral flora of dogs, which is likely the source of infection for this patient. In the literature, the spectrum of disease included sepsis/septic shock, fever of unknown origin, meningitis, cellulitis and respiratory tract infection. Asplenia is a major risk factor for developing infection and accounts for 80% of infections in the literature. Other risk factors include age over 40, cirrhosis, alcohol abuse, chronic lung disease, and immunocompromised patients. Fatalities occur in approximately 25% of cases.

Most organisms are sensitive to penicillin/beta lactamase combination antibiotics or extended spectrum cephalosporins. Carbapenem may be used for drug resistant organisms. Serious infections should be treated initially with intravenous antibiotics. Oral antibiotics can be used for more minor infections.

Conclusions: Capnocytophaga canimorsus is a zoonotic organism that can lead to very serious infections. Absence of clinical trials for therapy dictate that antibiotics be tailored to clinical response. A very careful and thorough history taking is necessary to make the diagnosis.