Community-acquired pneumonia associated with influenza co-infection caused by fusobacterium necrophorum: a case report and literature review

Background Fusobacterium necrophorum is a rare pathogen often associated with community-acquired pneumonia (CAP), especially when compromising healthy adults. This case report presents the first documented case of CAP caused by F. necrophorum in a young individual, providing valuable insights for the diagnosis and treatment of similar cases. Case presentation The patient, initially diagnosed with influenza, developed CAP caused by F. necrophorum . Despite one week of outpatient treatment with moxifloxacin, symptoms persisted, leading to hospitalization. Treatment with piperacillin tazobactam/imipenem and doxycycline, targeting atypical pathogens, did not result in improvement after admission. Conventional diagnostic methods failed to identify the causative pathogen, but metagenomics next-generation sequencing of bronchoalveolar lavage fluid confirmed it to be F. necrophorum . The patient showed significant improvement after ten days of targeted treatment with ornidazole and imipenem/piperacillin tazobactam and was discharged. Conclusion Uncommon pathogens, such as F. necrophorum , should be considered as potential culprits in young individuals with CAP when conventional cultures yield negative results but there is a strong suspicion of infection, especially if initial antibiotic therapy is ineffective.