Diagnosis and management of mixed Chlamydia abortus and psittaci pneumonia guided by metagenomic next-generation sequencing: a case report

Background Chlamydia abortus p rimarily causes abortion and stillbirth in animals and is associated with pregnancy-related complications in humans. However, it is an extremely rare cause of pneumonia in humans. While Chlamydia psittaci is a well-established respiratory pathogen, pneumonia resulting from a co-infection with both species has not been previously reported. Case presentation A 57-year-old male presented with fever, cough, and shortness of breath. Imaging revealed extensive pulmonary inflammation and consolidation, which rapidly progressed to respiratory failure. Metagenomic next-generation sequencing (mNGS) of bronchoalveolar lavage fluid (BALF) confirmed a mixed infection with Chlamydia abortus and Chlamydia psittaci . Following the early initiation of targeted doxycycline therapy, the patient’s clinical symptoms and pulmonary imaging showed significant improvement, leading to a full recovery and hospital discharge. Conclusions To our knowledge, this study reports the first case of atypical pneumonia caused by a mixed Chlamydia abortus and Chlamydia psittaci infection in a male patient, thereby expanding the clinical spectrum of these zoonotic pathogens. The case exhibited a “clinical-imaging dissociation,” characterized by severe radiographic changes alongside relatively mild clinical symptoms. When conventional diagnostic methods failed to identify the pathogens, mNGS provided a rapid and precise diagnosis. Guided by this result, early targeted therapy with doxycycline achieved a marked therapeutic effect, preventing progression to severe disease and an adverse outcome. Trial registration Not applicable.