Thoracic empyema caused by Prevotella spp. diagnosed using 16S rDNA sequence analysis.

We describe a case of thoracic empyema in a 76-year-old male with complication of diabetes mellitus and hypertension. His chief complaints were fever and chest pain. The patient was diagnosed as pleural infection according to the pulmonary computed tomography (CT) scan and laboratory results. The patient had persistent fever after the treatment of continuous percutaneous drainage and 1 week of intravenous moxifloxacin. He was then misdiagnosed as tuberculous pleuritis and still had fever after the treatment of 2 weeks' antituberculosis drugs. Repeated cultures of sputum, blood, bronchoalveolar lavage fluid and pleural fluid were all negative. A gram-negative bacillus was found in the pleural pus Gram stain, and it was identified as Prevotella spp. by 16S ribosomal DNA (rDNA) sequence analysis. The patient recovered after further treatment, including CT-induced pleural drain and intravenous imipenem. Totally, he received 2-week imipenem and 1-month metronidazole therapy from the day he was diagnosed with empyema to the termination of treatment. On the subsequent 2-month and 6-month follow-up visits, no recurrence has been reported for this patient. Routine microbiological methods are important in diagnosis of pleural infection, but they have limitations in some cases, especially for anaerobe. Molecular assay based on 16S rDNA is helpful in detecting causative organisms of thoracic empyema.