The patient was a 69-year-old male farmer who presented to a local hospital with right-sided chest pain, cough, sputum production, and fever for one week. Chest computed tomography (CT) at the local hospital showed multiple right pleural effusions and pneumothorax with right lung atelectasis. This patient had a cerebral infarction a year prior to this visit, with a slight decrease in right-sided muscle strength. He had a history of hypertension for several years and was receiving amlodipine benzoate with poor blood pressure control. The patient denied any history of other chronic diseases such as coronary heart disease, diabetes mellitus and malignancy. He had a 30-year history of smoking, 1 pack/day, had quit smoking for a year, and denied alcoholism. The patient was transferred to our hospital on October 17 after ineffective treatment with anti-infection (details unknown) and oxygen therapy.
The patient's vital signs on admission were as follows: temperature, 37.4 C; heart rate, 81 beats/min; breathing rate, 24 beats/min; and blood pressure, 165/85 mmHg. His consciousness was clear, and oxygen saturation was 85% (air). Reduced respiratory motility, decreased breathing sounds, and wet rales were observed on the right side. Both the lower extremities were moderately edematous. His right limb muscle strength was of grade V. Routine blood test showed leukocytes 13.5x109/L (normal range 3.5-9.5x109/L), neutrophils 12.4x109/L (normal range 1.4-7.12x109/L), hemoglobin 82 g/L (normal range 130-175 g/L) and normal eosinophils. Blood biochemistry showed only 18.1 g/L of albumin (normal range 40-55 g/L) and mildly elevated liver and kidney function parameters. PCT 4.88 ng/mL (normal range 0-0.05 ng/mL) and CRP 456 mg/l (normal range 0-8 mg/L) were observed. Serum GM and BDG levels were normal. T-SPOT. TB and ANA profiles were negative. T cell subsets and serum immunoglobulins were within normal limits. The chest CT on admission is shown in Figure 1. 
On day 2 of hospitalization, 700 mL of celiac fluid was extracted via closed chest drainage. Pleural fluid tests showed 19.6 g/L total protein, 4.9 g/L albumin, LDH 4700 IU/L (serum normal range 109-245 U/L), and ADA 183.4 U/L (serum normal range 2-17 U/L). The pleural fluid celiac characterization test results were negative. Pleural fluid CEA was within normal limit. Levantine tests were positive, with a nucleated cell count of 273.6x109/L (pleural fluid normal range <500x106/L) and 92% neutrophilic. A protozoan slightly larger in size than leukocytes, oval in shape, with rotational movement, was microscopically observed on a wet smear of pleural fluid. Suspected T. tenax was observed (Figure 2). 
On day 3 of hospitalization, intravenous infusion of metronidazole (0.5 g, q8h) combined with piperacillin tazobactam (4.5 g, q8h) was started. Thoracoscopy was performed on day 4 of hospitalization. Yellow flocculent pus was seen and aspirated. Adhesions on the pleural surface and granulation tissue were also visible. The adhesions were partly released and a biopsy of the mural pleura was performed. Pathological examination suggested fibrous connective tissue and many inflammatory fibrin-like exudates. After the operation, the patient felt relieved with chest pain and cough, and continued with closed thoracic drainage. Bronchoscopy was performed on day 5 of hospitalization, and mucous secretions were seen in the right lower lobe, where they were suctioned and lavaged.
On day 6 of hospitalization, the patient agreed to complete mNGS, and pleural fluid was sent for mNGS. The following day, the results were reported as 387 sequences of T. tenax, and 2,139,183 sequences of Porphyromonas endodontalis with a relative abundance of 70.73%. At this time, the diagnosis was clear of right-sided encapsulated pyopneumothorax, T. tenax and Porphyromonas endodontalis coinfection, type I respiratory failure, hypertension, and sequelae of cerebral infarction.
On day 8 of hospitalization, the patient experienced nausea and vomiting during the intravenous infusion of metronidazole, which was considered an adverse drug reaction. Symptomatic treatment was administered, and metronidazole was replaced to levonidazole intravenous infusion (0.5g, q12h). No further gastrointestinal reactions occurred after medication adjustment. The daily chest drainage fluid gradually became clearer and the volume decreased. Ultrasound examination of the pleural fluid showed that the right pleural fluid was separated. Multiple intrapleural injections of urokinase were administered.
Subsequently, the pleural fluid was rechecked several times and no more Trichomonas was detected. The blood culture results were negative. On day 24 of hospitalization, the patient was discharged after significant resolution of the chest lesion (Figure 3) and improvement of the inflammatory indicators. The patient was followed-up for 6 months without any chest infections.