The Correct Answer is A!

 

A 37-year-old white veterinarian presents in the emergency department for evaluation of fever and pain in his right hand. Yesterday, he was bitten on the hand by an injured dog. The patient required a splenectomy one year ago due to a ruptured spleen sustained in a motor vehicle accident. He is up to date with his pneumococcal, meningococcal, and haemophilus influenza type B vaccinations. On examination, his temperature is 39.2 C; pulse, 140 beats per minute; and blood pressure, 90/50 mm Hg. He is toxic appearing. His hand is red, swollen, warm, and tender.

Which of the following is the most likely organism responsible for his clinical picture?

A. Capnocytophaga canimorsus
B. Erysipelothrix rhusiopathiae
C. Aeromonas hydrophila
D. Bartonella henselae

 

Rationale:

Capnocytophaga canimorsus is the most likely diagnosis because Capnocytophaga canimorsus (Latin for “dog bite”), formerly known as CDC group DF2, is a facultative anaerobic gram negative bacillus that colonizes the mouths of dogs. The organism can cause soft tissue infections following dog bites and has been reported to cause sepsis in splenectomized patients. Capnocytophaga cynodegmi (Greek for “dog bite”) can also cause soft tissue infection following dog bite.

Erysipelothrix rhusiopathiae, Aeromonas hydrophila, and Mycobacterium marinum are unlikely diagnoses because Aeromonas hydrophila causes an acute soft tissue infection following exposure to freshwater or leeches, Erysipelothrix rhusiopathiae causes an acute soft tissue infection on the hands of fishermen and butchers, and Mycobacterium marinum causes a slowly progressive fish-tank granulomatous and lymphangitic infection of the extremities. None of these are particularly associated to dog exposure or more serious in splenectomized patients.

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