Abstract:Chlamydia pecorum (C. pecorum)is a Gram-negative obligate intracellular pathogen belonging to the Chlamydiaceae family. It can infect a wide range of animals, including sheep, goat, cattle, and wild animals. Human infection with C. pecorum is rare and without specific clinical symptoms. A 75-year-old male patient was diagnosed with severe community-acquired pneumonia, respiratory failure, shock, and acute kidney injury due to abdominal pain, nausea, vomiting, diarrhea, fever, and shortness of breath. The patient had a history of close contact with sheep, and chest CT showed inflammatory exudation, patchy shadows in the right lung, and consolidation in the left lung. C. pecorum was detected from patient's bronchoalveolar lavage fluid through metagenomic next-gene-ration sequencing (mNGS), combined with clinical manifestations and medical history, the patient was confirmed with severe pneumonia caused by C. pecorum and multiple organ failure. Despite targeted anti-infective and comprehensive treatment, the patient's condition didn't improve significantly and he was automatically discharged. This paper reports the diagnosis and treatment processes of this case, aiming to increase clinical awareness on C. pecorum infection, to take targeted treatment at the early stage, and to reduce the risk of mortality.