Bloodstream infections by zoonotic Capnocytophaga species: A review of reported cases, 2016-2025.

Zoonotic Capnocytophaga species are fastidious, Gram-negative bacteria naturally residing in the oral cavities of dogs and cats. Transmission to humans occurs via bites, scratches, or close contact like licks. While infections are rare, they can cause severe disease, with septicemia being the most frequent presentation. This review evaluated all published documented cases of zoonotic Capnocytophaga bloodstream infections (BSIs) between 2016 and 2025. A total of 100 studies involving 102 patients with zoonotic Capnocytophaga BSIs were identified. The median patient age was 60 years and most (61.8%) were male. Comorbidities were common in 80.4% of the patients. Almost one-third of the patients were immunosuppressed mostly due to asplenia and alcohol use disorders. Infections were most commonly secondary to dog bites, licks, and close exposure. Identification of the pathogen was most frequently performed by matrix-assisted laser desorption/ionization time-of- flight mass spectrometry (MALDI-TOF MS) (51.6 %) and C. canimorsus was the predominant species (93.1%). Sepsis was the most frequent clinical presentation. Severe complications included meningitis, infective endocarditis, disseminated intravascular coagulation, and purpura fulminans leading to symmetrical peripheral gangrene. All 102 patients received antibiotics. Treatment frequently involved administration of third-generation cephalosporins, carbapenems and β-lactams combined with β-lactamase inhibitors. The mortality rate attributed to the infection was 20.5%. Zoonotic Capnocytophaga BSIs are rare but highly fatal. Diagnosis is challenging because the organism is fastidious, grows slowly, and presents with unspecific symptoms. Early detection relies on identifying specific risk factors, applying molecular methods for rapid species identification, and immediately initiating broad-spectrum empiric antibiotics.