Pleural empyema caused by Streptococcus intermedius and Fusobacterium nucleatum - a distinct entity of pleural infections
Background Many community-acquired pleural infections are caused by facultative and anaerobic bacteria from the human oral microbiota. The epidemiology, clinical characteristics, pathogenesis and aetiology of such infections are little studied. The aim of the present prospective multicenter cohort study was to provide a thorough microbiological and clinical characterization of such oral-type pleural infections, and to improve our understanding of the underlying aetiology and associated risk factors.  Methods Over a 2-year period, we included 77 patients with community-acquired pleural infection, whereof 63 (82%) represented oral-type pleural infections. Clinical and anamnestic data were systematically collected, and patients were offered a dental assessment by an oral surgeon. Microbial characterizations were done using next-generation sequencing. Obtained bacterial profiles were compared to microbiology data from previous investigations on odontogenic infections, bacteraemia after extraction of infected teeth, and community-acquired brain abscesses.  Findings From the oral-type pleural infections, we made 267 bacterial identifications representing 89 different species. Streptococcus intermedius and/or Fusobacterium nucleatum were identified as a dominant component in all infections. We found a high prevalence of dental infections among patients with oral-type pleural infection and demonstrate substantial similarities between the microbiology of such pleural infections and that of odontogenic infections, odontogenic bacteraemia and community-acquired brain abscesses.  Interpretation Oral-type pleural infections is the most common type of community-acquired pleural infection. Current evidence supports haematogenous seeding of bacteria from a dental focus as the most important underlying aetiology. Streptococcus intermedius and Fusobacterium nucleatum most likely represent key pathogens necessary for establishing the infection.  Funding Haukeland University Hospital