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 associated with community-acquired pneumonia (CAP), particularly among healthy adults. This case report presents a rare 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 was initially diagnosed with influenza, and subsequently developed CAP caused by F. necrophorum. Despite one week of outpatient treatment with moxifloxacin, the symptoms persisted, leading to hospitalisation. Treatment with piperacillin tazobactam/imipenem and doxycycline, which target atypical pathogens, did not result in improvement after admission. Conventional diagnostic methods failed to identify the causative pathogen; however, metagenomic 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.