The first case of deep neck abscess due to Filifactor alocis co-infected with Eggerthia catenaformis, Parvimonas micra, and Streptococcusconstellatus.

Filifactor alocis, an anaerobic Gram-positive rod, has garnered interest from its association with periodontal disease. Extraoral infections by F. alocis are rare; only seven cases have been reported. We report the first case in which we identified F. alocis as one of the causative organisms of a deep neck abscess. A 71-year-old male on hemodialysis came to our hospital with a fever and left buccal pain. The patient's left neck was swollen, and contrast-enhanced computed tomography showed an abscess with gas extending from the left cheek to the deep neck. We diagnosed the patient with a deep neck abscess and performed an urgent neck drainage. We isolated F. alocis, Eggerthia catenaformis, Parvimonas micra, and Streptococcus constellatus in the abscess and identified them using matrix-assisted laser desorption ionization-time of flight mass spectrometry. Blood cultures were negative. We initiated treatment with piperacillin-tazobactam and vancomycin. The patient improved but developed a hemorrhagic duodenal ulcer on the third day of admission. We attempted endoscopic hemostasis, but the patient's bleeding continued. Ultimately, he died of the duodenal ulcer hemorrhage on the sixth day of admission. This is the first case of F. alocis detected in a deep neck abscess.