A 74-year-old man was admitted to the Department of Respiratory and Critical Care Medicine of the First Affiliated Hospital of Chongqing Medical University on 25 March 2022 with a complaint of dry cough, fever, and intermittent chest pain for 17 days and shortness of breath after activity for 4 days. He denied night sweats and weight loss. There was no history of hemoptysis, recent contact with tuberculosis or irritant gas, or any other underlying health conditions, except for 20-year smoking history. When the symptoms first occurred, the patient underwent a series of computed tomography (CT) scans. At that time, he was treated with amoxicillin clavulanate potassium for 4 days and with levofloxacin for 6 days (Figure 1). His chest pain was significantly relieved and his temperature returned to normal. However, the patient continued to cough intermittently and experience shortness of breath after activity. As shown in Figure 2, consecutive CT images showed an increasing number of nodules and exudative inflammatory lesions with a newly emerged pleural effusion. Physical examination indicated normal vital signs (Body temperature: 36.2 C, Pulse rate: 70/min, Respiratory rate: 20/min, Blood pressure: 146/74 mmHg) but asymmetric breath sounds without rales or wheezing. Blood gas analysis indicated a Pondus Hydrogenii (PH) of 7.48, a Partial Pressure of Carbon Dioxide (PCO2) of 37 mmHg, Oxygen Permeance (PO2) of 73 mmHg, Bicarbonate (HCO3-) of 27.6 mmol/L, and oxygen saturation (SO2) of 96%. His leukocyte levels were normal, but his erythrocyte sedimentation rate was elevated, at 61 mm/h.
According to his clinical symptoms and the dynamic changes observed in chest CT, we highly suspected an infectious lung disease. Because of the non-specific clinical manifestations, pathogenetic examination was very important for this patient. Therefore, we collected microbiological samples and performed routine bacteria culture. The GeneXpert MTB/RIF assay and mNGS were performed on 29 March 2022, 4 days after admission, in an attempt to identify pathogenic bacteria. Meanwhile, his antibiotic treatment was switched to moxifloxacin to better fight against Gram-positive bacteria and covered the antibacterial spectrum of anaerobic bacteria. As shown in Table 1, the laboratory tests, such as Galactomannan Antigen Testing (GM), beta-D-glucan fungal antigen test (G test), and tests for cryptococcal pod antigen, were negative; however, the patient was positive for mycoplasma antibody (IgM). The pleural effusion was exudate consisting of 44% leukocyte. Samples of it were sent for routine bacteria culture and were analyzed using the GeneXpert MTB/RIF assay and mNGS. BALF samples were also subjected to routine bacteria culture and GeneXpert MTB/RIF assay. All samples returned negative in all of the tests except mNGS, which identified four specific reads of P. micra with 9% relative abundance from pleural effusion samples.
To search for the source of infection, enhanced CT of the oropharyngeal and abdomen as well as cardiac ultrasound were conducted. A medical history inquiring about toothache, periodontitis, and oral invasive operations was conducted, and the patient denied underlying oral diseases. No abscesses were detected in any CT image, and cardiac ultrasound revealed a lack of bacterial emboli. However, an examination of the oral cavity indicated that most tooth crowns of this patient were missing, while the roots remained. Oropharyngeal CT also suggested multiple root remnants with partial alveolar bone resorption. Further inquiries revealed that the patient wore dentures for an extended period of time; these were cleaned and soaked in normal tap water that was not changed every day. Based on the poor oral hygiene and colonization of the oral cavity with P. micra, we intended to conduct mNGS to analyze oral and lung pathogens. However, because of the high cost of mNGS, we had to analyze the oral and lung microbiome by 16s rRNA gene sequencing. Interestingly, the results identified Parvimonas not only in the oral cavity but also in the BALF (Figure 3). Compared to the oral flora of healthy men, the patient's alpha diversity of the oral cavity was significantly reduced (Figure 3). Based on these factors, we speculated that the oral cavity could have been the potential infection source. Moxifloxacin treatment was continued. Fortunately, a follow-up chest CT on 4 April 2022 showed complete absorption of pleural fluid and significant resolution of the exudative lesions (Figure 2). Given that the adjusted treatment was effective, moxifloxacin was continued for 3 more months. Finally, a chest CT on 15 June 2022 showed almost total resolution of the lung lesion (Figure 2).