Metagenomic Next-Generation Sequencing Reveals Tannerella forsythia in Lung Abscesses: A Retrospective Case Series Linking Smoking, Oral Health, and Diagnostic Challenges.

Purpose: Tannerella forsythia (T. forsythia) is a Gram-negative anaerobic bacterium commonly found in the oral cavity of patients with periodontitis, but lung abscesses caused by this pathogen are extremely rare in the literature. This study aimed to characterize the clinical features, diagnostic challenges, and treatment outcomes of T. forsythia-associated lung abscesses through four case analyses.

Patients and methods: We retrospectively reviewed four patients treated between April 2023 and May 2024 with lung abscesses confirmed by chest computed tomography (CT) and T. forsythia detection via metagenomic next-generation sequencing (mNGS) of bronchoalveolar lavage fluid (BALF). Conventional cultures were performed but yielded negative results. Clinical data, including demographics, symptoms, imaging findings, and treatment regimens, were analyzed.

Results: All patients had oral diseases, and 75% were long-term smokers. The primary clinical manifestations were nonspecific respiratory symptoms, including cough, fever, chest pain, and hemoptysis. Chest CT revealed consolidation and cavitation in the upper lobes of the lungs. T. forsythia was successfully detected by mNGS of BALF, while conventional cultures failed to identify pathogens in all cases. All patients received combination antibiotic therapy based on metronidazole and piperacillin-tazobactam, with some cases requiring additional antibiotics. Following treatment, significant clinical improvement was observed, and follow-up imaging demonstrated gradual resolution of the lesions.

Conclusion: This study is limited by its small sample size and the lack of confirmatory tests, which warrant validation in larger prospective cohorts. Our findings highlight the advantages of mNGS in detecting fastidious pathogens (such as the anaerobic bacterium T. forsythia), providing new insights for the diagnosis of similar infections in the future. Additionally, the results identify smoking and poor oral health as common features that may be associated with the development of T. forsythia-associated lung abscesses.