Mycotic aneurysm caused by group B streptococcus: a cautionary tale of management problems and a rare organism.

We report a case of mycotic aneurysm of the femoral artery which highlights the diagnostic features and management problems of the condition. Our patient required emergency ligation of the artery for life-threatening haemorrhage and subsequently his leg was not viable. The alternative treatment options of simple ligation and excision versus ligation, excision and immediate bypass grafting of the artery are discussed. The causative organism, beta-haemolytic group B streptococcus (S. Agalactiae), is an extremely rare cause of embolic mycotic aneurysm. This rarity is unexplained and is surprising since this organism is a well-known cause of infective endocarditis, which can be complicated by mycotic aneurysms. Mycotic aneurysms may become more common because of the rise of intravascular drug abuse, which combines the risk factors of vessel trauma, endocarditis and immunosuppression, notably from HIV infection.