Clinical Characteristics of Five Cases of <i>Chlamydia psittaci</i> Pneumonia Diagnosed Using Metagenomics Next-Generation Sequencing

<b><i>Objective:</i></b> This study aimed to analyze the clinical characteristics of five cases of <i>Chlamydia psittaci</i> pneumonia diagnosed using metagenomics next-generation sequencing (mNGS) and to provide help for its diagnosis and treatment. <b><i>Methods:</i></b> Five patients who were admitted to the department of Respiratory and Critical Care Medicine of Beijing Aerospace General Hospital between June 2020 and December 2021 and diagnosed with <i>C. psittaci</i> pneumonia using mNGS were selected, including one case with severe pneumonia. We analyzed the clinical characteristics, epidemiology, laboratory results, treatment, and prognosis of the five participating patients. <b><i>Results:</i></b> The main clinical manifestations were high fever, dry cough, chest tightness, shortness of breath, and myalgia. All five patients had a history of contact with poultry. The white blood cell count was normal or slightly increased, the lymphocyte count was significantly decreased, and the percentage of neutrophil granulocyte, C-reactive protein (CRP), erythrocyte sedimentation rate, and procalcitonin were significantly increased. Chest computed tomography showed inflammatory infiltration and consolidation of one or more lung lobes, possibly accompanied by pleural effusion and liver function impairment. Bronchoscopy mainly showed congestion and edema of airway mucosa with less sputum in the airway. In all patients, we detected the nucleic acid sequences of <i>C. psittaci</i> in alveolar lavage fluid or sputum using mNGS and confirmed the diagnosis of <i>C. psittaci</i> pneumonia based on clinical manifestations and exposure history. After adjusting antibiotics to a moxifloxacin-based treatment regimen, the disease improved. The application of the mNGS assay enables us to make faster diagnoses of diseases so that timely medication can be administered, thus shortening the duration of a patient's illness. <b><i>Conclusion:</i></b> <i>C. psittaci</i> pneumonia has an acute onset, and fever and cough are common symptoms. A history of contact between the patient and birds is an important diagnostic clue; however, clinical symptoms and laboratory and imaging examinations lack specificity. The detection using mNGS of bronchoalveolar lavage fluid can quickly confirm the diagnosis and reduce missed diagnoses and misdiagnoses. Moxifloxacin-based therapy is effective, and patients require combination therapy if they have other bacterial infections.