A Case of Complicated Pneumonia Caused by Klebsiella ozaenae.

, a subtype of ,causes chronic upper respiratory tract infections, such as rhinitis and rhinoscleroma, and can also cause lethal infections. We report the case of a patient who developed pneumonia caused by . An 87-year-old man presented to our hospital with fever and chills. Physical examination revealed no findings other than bilateral crackles in the lower lung fields. Chest computed tomography (CT) showed infiltrative shadows in the lower left lung field. Moreover,  was detected in blood cultures. Based on the examination results, including radiography and blood culture, the patient was diagnosed with pneumonia caused by . On admission, the patient was treated with intravenous ceftriaxone (CTRX), but he did not recover. After determining the antibiotic susceptibility of , we stopped administering CTRX and started ampicillin/sulbactam (ABPC/SBT) treatment for two weeks. During the ABPC/SBT administration, a second chest CT showed a new infiltrative shadow in the upper left lung field. Despite these findings, the patient was discharged from the hospital as his vital signs were stable and his general condition was good. After two weeks of ABPC/SBT treatment, the patient was switched to minocycline and followed up. Although infections caused by  are rare, they can be life-threatening.  identification in a patient's blood culture indicates a potentially impaired immune system, prompting physicians to evaluate the patient's immune system.