Delayed-Onset Infectious Aortic Aneurysm Caused by Hypermucoviscous Klebsiella pneumoniae Detected on Reevaluation Contrast Computed Tomography

<i>Klebsiella pneumoniae </i>subsp. Pneumoniae (Kp) is a Gram-negative bacillus commonly encountered in clinical practice, often causing urinary tract infections and pneumonia. Kp includes classical strains (cKp) and hypervirulent strains (hvKp), the latter causing invasive syndromes, such as liver abscesses, endophthalmitis, and meningitis. HvKp is increasingly reported in East Asia, including Taiwan, and has occasionally been implicated in infectious aortic aneurysms (IAA). The hypermucoviscous phenotype of Kp (hmKp), identified by a positive string test, is strongly associated with hvKp. We report a case of sepsis caused by hmKp in a 65-year-old male. Although the patient initially responded to antibiotic therapy, low-grade fever and elevated inflammatory markers persisted. Reevaluation using contrast-enhanced computed tomography (CECT) revealed a delayed-onset IAA. The patient underwent emergency endovascular aneurysm repair (EVAR), followed by open aortic replacement (OAR), resulting in survival. This case highlights the importance of considering deep infections such as infectious aneurysms in patients with hmKp sepsis that fails to show expected clinical improvement despite appropriate treatment. Timely reevaluation with CECT is crucial for detecting life-threatening complications and enabling prompt, definitive management.