Severe community-acquired pneumonia complicated by co-infection with Chlamydia psittaci and ESBL-producing Escherichia coli: a case report

Abstract Background Chlamydia psittaci is an uncommon but potentially severe cause of community-acquired pneumonia (CAP), typically associated with exposure to birds. Co-infection with multidrug-resistant bacteria is rare and may complicate clinical management. Case presentation We report the case of a 71-year-old man with long-term pigeon exposure who presented with high fever, cough, and purulent sputum. He rapidly progressed to severe CAP, type I respiratory failure, and sepsis. Initial routine microbiological tests were negative. Bronchoalveolar lavage fluid metagenomic next-generation sequencing (mNGS) detected C. psittaci , and sputum culture grew extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli (ESBL-EC). Initial empiric therapy with piperacillin-tazobactam and doxycycline failed to control the disease. After treatment adjustment guided by mNGS and antimicrobial susceptibility testing, including piperacillin–tazobactam, doxycycline, and levofloxacin, combined with respiratory support and organ protection, the patient improved and was discharged. Conclusions This case highlights the importance of considering mixed infections, including drug-resistant bacteria, in severe CAP patients with avian exposure who fail empiric therapy. mNGS is a valuable tool for rapid etiological diagnosis in such complex cases. In addition, detection of multidrug-resistant organisms in respiratory samples should be interpreted cautiously, considering colonization, clinical correlation, and therapeutic response.