Canine-Associated Capnocytophaga canimorsus Bacteremia in an Older Adult Without Classical Immunosuppressive Risk Factors.

BACKGROUND Several Capnocytophaga species exist, some predominantly colonizing the human oral cavity and others residing in feline or canine oral flora. Capnocytophaga canimorsus is a gram-negative facultative anaerobe commonly found in the oral cavity of dogs and, less commonly, cats. C. canimorsus infections are rare in humans. Although beta-lactamase production has been described among Capnocytophaga species, it is less common in C. canimorsus; therefore, penicillin may remain appropriate when susceptibility is confirmed. CASE REPORT An older man was admitted to the Family Medicine Inpatient Service with erythema and edema of the right hand after sustaining a hand laceration several days prior to admission; the wound had been licked multiple times by his dog. The patient developed worsening erythema and tenderness of the dorsal right hand, accompanied by progressive leukocytosis. He was transitioned to intravenous ampicillin-sulbactam. Blood cultures grew C. canimorsus. Because beta-lactamase testing results were pending at discharge, the patient was prescribed oral amoxicillin-clavulanate. CONCLUSIONS C. canimorsus is a rare zoonotic pathogen but can cause severe disease, particularly in patients with cirrhosis, asplenia, or alcohol use disorder; in the present case, advanced age may have contributed to vulnerability through immunosenescence. Growth of gram-negative bacilli in aerobic or anaerobic blood cultures from patients with zoonotic exposure should raise clinical suspicion for this organism. When Capnocytophaga infection is suspected in a hospitalized patient, empiric treatment with ampicillin-sulbactam should be initiated while awaiting culture confirmation and susceptibility results.