Chlamydia psittaci pneumonia manifested as pulmonary nodules and cavitary lesions: a case report.

Background: Chlamydia psittaci pneumonia (CPP) typically presents with exudative and consolidative changes on chest computed tomography (CT), including lung consolidation, bronchial air trapping, pleural effusion, and ground-glass opacities. Here, we report an atypical case of CPP manifesting as pulmonary nodules and cavitary lesions, which was subsequently diagnosed through targeted next-generation sequencing (tNGS) of bronchoalveolar lavage fluid (BALF).

Case presentation: A previously healthy 16-year-old male adolescent developed a severe cough with scant mucoid sputum, nasal congestion, and rhinorrhea after cleaning his dormitory, with symptoms lasting nearly one month. Initial laboratory tests revealed normal infection-related markers, including white blood cell (WBC) count, interleukin-6 (IL-6), and procalcitonin (PCT), while chest CT showed pulmonary nodules and a small cavitary lesion. Based on the clinical presentation of persistent cough and the absence of significant inflammatory markers, empirical therapy with intravenous doxycycline was initiated, resulting in significant symptom improvement. After discharge, failure to follow the recommended dosing schedule and non-standardized use of oral doxycycline (including missed doses and co-administration with milk) compromised treatment efficacy. A follow-up CT demonstrated partial improvement in the right lung lesion but progression in the left, prompting a switch to cephalosporin, which proved ineffective. Referred to our hospital, bronchoscopy and tNGS of BALF identified Chlamydia psittaci (11 nucleic acid sequence reads), confirming psittacosis. A 14-day course of oral doxycycline led to significant clinical improvement and resolution of pulmonary lesions on follow-up imaging.

Conclusion: In clinical practice, CPP should be included in the differential diagnosis for patients presenting with pulmonary nodules and cavitary lesions on imaging, even in the absence of confirmed direct avian exposure. This consideration is particularly crucial when patients exhibit persistent respiratory symptoms coupled with poor clinical response to broad-spectrum antibiotic therapy.