Capnocytophaga canimorsus peritonitis in a simultaneous liver-kidney transplant recipient: a case report and review of the literature

• Capnocytophaga canimorsus is a rare cause of bacterial peritonitis, with prior cases reported almost exclusively in patients receiving peritoneal dialysis or with cirrhosis. • We report the first documented case of C. canimorsus peritonitis in a solid organ transplant recipient presenting with septic shock and culture-negative ascites. • Broad-range bacterial PCR using 16S rRNA gene sequencing identified C. canimorsus in peritoneal fluid after routine cultures were negative. • Close contact with pet dogs likely served as the exposure source, underscoring zoonotic risk in immunocompromised hosts. • This case supports the adjunctive use of molecular diagnostics in culture-negative bacterial peritonitis and highlights the importance of pet-exposure counseling in transplant recipients. Capnocytophaga canimorsus is a fastidious, capnophilic Gram-negative rod transmitted through exposure to the oral secretions of domesticated dogs and cats and may cause severe infection in immunocompromised hosts. Bacterial peritonitis due to C. canimorsus is rare and has been reported primarily in patients receiving peritoneal dialysis. We describe a 66-year-old man status post simultaneous liver and kidney transplantation who presented with septic shock, neutropenia, acute kidney injury, and worsening ascites. Peritoneal fluid analysis demonstrated neutrophilic ascites consistent with bacterial peritonitis, although cultures were negative. Blood cultures and broad-range bacterial polymerase chain reaction using 16S rRNA gene sequencing identified C. canimorsus , confirming the diagnosis. The patient reported close contact with pet dogs and improved with targeted beta-lactam therapy. This represents the first reported case of C. canimorsus peritonitis in a solid organ transplant recipient and highlights the diagnostic value of molecular testing in culture-negative peritonitis.