A 57-year-old presents to the emergency room with knee pain, gait disturbances and fever. His dog provides the decisive clue to the diagnosis.
A 57-year-old man presents to the emergency department with left knee pain, difficulty walking and fever – symptoms have lasted for 3 days, he says. The patient reports using intravenous drugs and is already suffering from chronic Hepatitis C and HIV infections preloaded. The infections were diagnosed regarding 30 years ago. However, the patient is in good immune control: that is, he has no detectable viral load and the CD4 was 879 mm-3. In addition, the man wears a bilateral hip prosthesis and suffers from mixed sensorimotor polyneuropathy. Although the patient lives with a dog, it is said to be very peaceful – the 57-year-old does not report any bites or scratches, only licking.
The first result
Initial examination reveals severe pain, erythema, and swelling in the left knee and thighs, with no outward signs of cellulitis. The attending physicians lead a Arthrocentesis by, with an inflammatory synovial fluid with 44,300 leukocytes mm-3 (80% neutrophils). The blood test values also look similar: They are 12,700 leukocytes mm-3 with 80% neutrophils and one reactive C protein level of 262 mg/l. The finding points to an infectious disease, which is why the patient is initially treated with intravenous Ceftriaxone and cloxacillin – the administered dose was 2 g/50 ml every 24 h and 1 g/50 ml every 6 h. Despite the treatment, the severe pain does not subside, which is why the doctors CT of the lower extremities.
Lower extremity CT scan with intravenous contrast. Credit: Fecilla et al.
Image shows signs of inflammatory arthritis with collections located primarily between the medial calf and the Soleus extend in the left leg. Deep vein thrombosis cannot be detected. Despite findings of bone infarction in both knees, there is no evidence of one Osteomyelitis.
It’s a zoonosis
In order to determine which infection is actually involved, the initially obtained synovial fluid is examined for laboratory diagnostics. The result: Capnocytophaga canimorsus Serotyp A.
C. canimorphus is a slow-growing, facultatively anaerobic, gram-negative, rod-shaped bacterium. It occurs naturally in the oropharyngeal flora of healthy dogs and cats. It can be zoonotically transmitted to humans through animal bites, scratching, licking, or even through close contact. The serotypes A, B and C seem to be more virulent than serotypes D-I. Although they are rare in dogs (<8%), they represent the vast majority of human isolates.
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It is known that C. canimorphus severe infections with a mortality rate of regarding 30%. Typically, these infections are caused by a Sepsis characterized by septic shock or a disseminated intravascular coagulation (DIC) can get complicated. Meningitis and endocarditis have also been described, although osteoarticular infections are less common. C. canimorphus is largely sensitive to all Betalactamen, Clindamycin and Tetracyclines.
Difficult clinical course
Five days following hospital admission, the patient undergoes surgical cleaning and drainage of the accumulations Arthrotomie. And C. canimorphus was found to be responsible for the sepsis, the treating staff set the antibiotic therapy to intravenous Piperacillin/Tazobactam (4 g/0.5 g every 8 h).
However, the clinical course is unfavorable, with increasing pain and persistent mild fever over 4 weeks. The 57-year-old therefore needs a second surgical cleaning just 13 days later. Also a big one hematoma is observed and emptied. After one month, the treating physicians switch the antibiotic therapy to intravenous ceftriaxone (2 g every 24 h) for 10 days. Finally, the patient is given orally Clindamycin (600 mg every 8 h) for de-escalation. Two months following admission, his clinical condition is improving and the man can be discharged following nine weeks of antibiotic therapy.
“In summary, the incidence of C. canimorphus-Infections will increase over time due to reliable new diagnostic methods, a more susceptible population and the increasing popularity of keeping pets”, this is the conclusion of the authors.
Image source: Sebin Laluunsplash
