Methicillin-Resistant Staphylococcus aureus (MRSA) Strikes Deep: Infected Femoral Aneurysm in a Patient With Deep Vein Thrombosis.

Infectious (mycotic) aneurysms are rare but potentially life-threatening complications of bacteremia. They account for a small percentage of all aneurysms. Early recognition is essential to prevent catastrophic outcomes. We report a case of a 53-year-old man with a history of methicillin-resistant Staphylococcus aureus (MRSA) nasal abscess who presented with fever, vomiting, and progressive right leg swelling. He was febrile and tachycardic. Labs showed neutrophilic leukocytosis (white cell count of 17.4 x 10⁹/L), elevated C-reactive protein (CRP; 127.4 mg/L), and positive blood cultures for MRSA. Doppler ultrasound revealed acute deep vein thrombosis (DVT) in the right femoral and deep veins. Despite vancomycin, he had persistent bacteremia, and antibiotics were escalated to ceftaroline and daptomycin. Computed tomography (CT) angiography obtained for worsening leg swelling revealed a 6.4 x 6.3 x 7.3 cm right superficial femoral artery aneurysm. He underwent urgent excision, ligation, and bypass, followed by serial surgical washouts. The infectious aneurysm likely resulted from local vascular inflammation caused by an infected thrombus or hematogenous seeding. Persistent fever and worsening leg swelling despite therapy warranted further imaging. MRSA is a well-documented cause of mycotic aneurysms and requires aggressive treatment. In patients with bacteremia and DVT who deteriorate despite treatment, infectious aneurysm should be considered. Early imaging and multidisciplinary care are crucial in preventing rupture and limb loss.