Abstract: Objective To study the clinical characteristics, laboratory tests, imaging findings, and treatment strategies for Chlamydia psittaci pneumonia in elderly patients. Methods A retrospective analysis was performed for the treatment of 28 case of Chlamydia psittaci pneumonia diagnosed via metagenomic next-generation sequencing technology (mNGS) from August 2020 to August 2023 in our hospital. The data of all patients on medical history, clinical manifestations, laboratory tests, chest computer tomography (CT) performance, treatment and prognosis of patients were collected. Results Among the 28 patients, there were 16 males and 12 females, with a mean age of (72.1±8.8) years. There were three patients who raised pigeon and four patients who raised parrot. The onset to admission interval was (5.6±3.0) days, and hospital stay was (14.3±4.3) days. The clinical manifestations included fever, cough, sputum, palpitations and diarrhea. The laboratory tests: white blood cell count was (6.8±2.2) ×10⁹/L, the proportion of neutrophils was (81.1±8.7）×10⁹/L, C-reactive protein level was 155（126.5）mg/L. Chest CT showed a variety of manifestations: consolidation, consolidation with ground-glass opacity, ground-glass opacity, bronchial inflatable sign, anti-halo sign, pleural effusion, etc. The CURB-65 score was (1.43±0.84), and the PSI score was (109.75±32.97). In terms of treatment, 16 patients were treated with moxifloxacin alone, 5 patients with levofloxacin alone, 4 patients with piperacillin tazobactam and minocycline, 2 patients with carbapenem plus minocycline, and 1 patients with carbapenem plus moxifloxacin. There were 5 patients received high-flow oxygen inhalation. All patients recovered. The relationship between hospitalization time and CURB -65 score, PSI score, gender, C-reactive protein, and chest CT findings: there was statistically significant correlation between PSI score and hospitalization time; C-reactive protein has statistical significance with hospitalization time; bilateral lobar involvement and hospitalization time were statistically significant; the rest were not statistically significant. Conclusion As the CRP and PSI score increase and bilateral lung lobes are affected, the patient’s hospitalization time prolongs, and quinolone antibiotics are effective against Chlamydia psittaci pneumonia. Elderly patients have multiple underlying diseases, and community-acquired pneumonia is prone to multiple organ dysfunction and progression to severe illness. Early identification of pathogens is necessary to shorten the course of the disease and improve prognosis.

Key words: chlamydia psittaci, community-acquired infection, metagenomic, second-generation sequencing