Rapid Progression of Aortitis Caused by Methicillin-Sensitive Staphylococcus Aureus in a Patient With Pneumonia: A Case Report.

Infected aortic aneurysm is a rare but fatal disease that occurs through various mechanisms. In this report, we describe the case of a patient who was hospitalized for acute pneumonia and developed an infected aortic aneurysm in the descending aorta during the hospitalization. A 73-year-old Japanese man presented to the emergency department with a chief complaint of fever. He had a history of chronic renal failure due to nephrosclerosis and was on regular hemodialysis three times a week. The patient presented with an elevated inflammatory response, anemia, and low platelet counts after various tests. Computed tomography (CT) showed ground-glass opacity in the left lung with a small amount of pleural effusion, leading to a diagnosis of pneumonia. The patient was admitted to the hospital on the same day, and a course of antibiotics (ceftriaxone [CTRX]) was started. On the fourth day of hospitalization, methicillin-susceptible Staphylococcus aureus (MSSA) was detected in the blood sample, which was collected from the patient on the day of admission. The patient was treated for MSSA pneumonia and bacteremia, and the antibiotics were changed to cefazolin (CEZ). Treatment with antimicrobials resulted in a negative blood culture retest on day 5 and improvement of the inflammatory response. On the 12th day, improvements in pneumonia and pleurisy were observed on the CT scan; however, an abnormal bulge was seen on the dorsal side of the descending thoracic aorta with suspected partial vessel wall disruption, suggesting a ruptured infected aortic aneurysm. Despite treatment with antibiotics, the thoracic descending aortic aneurysm continued to dilate with progressing rupture, and the patient died on the 25th day of hospitalization. This is the first report of an infected aneurysm caused by Staphylococcus aureus, despite a negative blood culture. Patients at high risk might develop infected aneurysms, and the possibility of rapid dilation should always be considered.