Chlamydia psittaci pneumonia in 23 patients: a single-center retrospective case series

To describe the clinical, laboratory, imaging, treatment, and outcome characteristics of patients with pneumonia in whom Chlamydia psittaci was detected by targeted next-generation sequencing (tNGS) of bronchoalveolar lavage fluid (BALF) and to explore genotype-phenotype associations.

This single-center retrospective descriptive case series included 23 patients treated at Qingyang People's Hospital, Qingyang Second People's Hospital, Xifeng District People's Hospital between May 2024 and September 2025. All had clinical and radiological evidence of pneumonia and C. psittaci detected in BALF by tNGS. Stored residual BALF from 13 patients underwent post hoc C. psittaci-specific quantitative PCR (qPCR).

Ten patients had severe pneumonia and 13 had common pneumonia; 12 (52.17%) reported bird or poultry exposure. Compared with the common pneumonia group, the severe pneumonia group had lower platelet counts and serum albumin levels and higher procalcitonin levels. Severe cases more often had bilateral lung involvement and pleural effusion. In the exploratory genotype comparison, GCF_000415765 was associated with higher alanine aminotransferase and lower albumin than GCF_000415825; the between-group difference in D-dimer was not statistically significant. Of 13 stored residual BALF specimens tested by qPCR, 7 showed target amplification (53.85%; exact two-sided 95% confidence interval, 25.13%-80.78%).

This selected case series describes severity-related clinical and radiological features and exploratory genotype-phenotype patterns. The qPCR findings provide additional microbiological evidence in a subset but do not validate tNGS. Prospective studies that enroll tNGS-positive and tNGS-negative patients and apply an independent reference standard to all participants are needed.