Psittacosis Complicated with Organizing Pneumonia: A Case Report and Literature Review

Qiao Li^1,2Nan Su^1*Xu Sun¹Wenwen Du¹Xinyu Jiang¹Yehan Zhu¹Wei Lei¹

• ¹The First Affiliated Hospital of Soochow University, Suzhou, China, suzhou，china, China
• ²Suzhou University, Suzhou, China

Background: Secondary organizing pneumonia (SOP) may develop following infections. Psittacosis, caused by Chlamydia psittaci (C. psittaci), is a zoonotic disease transmitted from birds to humans. It can present with a wide spectrum of symptoms, ranging from mild flu-like illness to life-threatening severe pneumonia. Cases of C. psittaci infection complicated by organizing pneumonia (OP) are rarely reported, and delayed treatment may pose a life-threatening risk. Methods: We report a case of C. psittaci pneumonia complicated by OP. To identify additional cases and clarify the clinical features of this condition, a literature search was conducted using the PubMed and Embase databases for the period from January 1995 to May 2025. The search included the following keywords: "psittacosis," "Chlamydia psittaci," "chlamydia," "organizing pneumonia," and "bronchiolitis obliterans with organizing pneumonia." Results: A 66-year-old male with a history of poultry farming presented with fever, cough, sputum production, and hemoptysis. Empirical antimicrobial therapy with ceftizoxime was ineffective. To identify the etiology of the pulmonary lesions, bronchoscopy was performed, and C. psittaci infection was confirmed by metagenomic 2 next-generation sequencing (mNGS) of bronchoalveolar lavage fluid (BALF). Although the lesions partially resolved after moxifloxacin therapy, the patient experienced recurrent episodes. Chest CT revealed migratory lesions, which are uncommon in C. psittaci pneumonia. Further pathological examination of the specimen confirmed the diagnosis of OP. The patient's condition improved following corticosteroid therapy. A review of the literature indicated that none of the three previously reported cases were definitively diagnosed at initial admission; all presented primarily with fever and cough. One case progressed to severe pneumonia and resulted in death. Conclusion: OP caused by C. psittaci pneumonia presents with nonspecific symptoms and signs, making early diagnosis challenging. During treatment of C. psittaci pneumonia, if empirical anti-infective therapy shows no response after three days, or if imaging reveals features such as consolidation, migratory lesions, or a reverse halo sign, the possibility of concurrent OP should be considered. Pathological examination is recommended in such cases to avoid missed diagnosis and to ensure timely intervention.