Clinical characterization of Chlamydia psittaci infections detected by targeted next generation sequencing in a Chinese tertiary hospital.

BACKGROUND

Psittacosis is a zoonotic disease caused by Chlamydia psittaci (C. psittaci). Its clinical symptoms are nonspecific, ranging from influenza-like symptoms to severe pneumonia. Thus, it is often ignored and underreported. To date, the report of C. psittaci infections detected by targeted next generation sequencing (tNGS) is still limited.

METHODS

tNGS was performed on the platform of Vision Medicals in patients with fever or respiratory infections from August 2024 to August 2025 in our hospital. The specimens included blood and bronchoalveolar lavage fluid (BALF). C. psittaci infection was confirmed by real-time PCR. Detailed clinical data of the included patients were collected and analyzed from electronic medical records.

RESULTS

Eight psittacosis patients were detected by tNGS and confirmed by real-time PCR. The median age of 8 patients was 69 years (range: 46-86 years). Five patients (62.5%) had a history of exposure to birds. Clinical symptoms included fever, cough, fatigue, headache and dyspnea. Patients exhibited normal or elevated white blood cell (WBC) counts with decreased lymphocyte counts. C-reactive protein (CRP), procalcitonin (PCT), and interleukin-6 (IL-6) levels were significantly elevated. The majority of patients (87.5%, 7/8) developed hepatic dysfunction. Pulmonary lesions were multi-lobar, presenting as consolidation, ground glass opacities and air bronchogram signs, with pleural effusion occurred in some cases. Following confirmation of C. psittaci infection, targeted antimicrobial therapies with tetracyclines (tigecycline or omacycline) were administered. All patients demonstrated significant reductions in inflammatory markers after treatments, with clinical symptoms improving until resolution. Follow-up chest computed tomography (CT) scans showed resolution of infection foci. All patients ultimately recovered and were discharged.

CONCLUSION

tNGS is a promising tool for rapidly detecting C. psittaci infections. Early diagnosis of psittacosis with subsequently targeted therapies improved patients' outcome.