Mediastinal abscess and bacteremia due to Streptococcus dysgalactiae complicated by aorto-esophageal fistula leading to death with massive bleeding in a 70-year-old Japanese man with gastric cancer

Streptococcus dysgalactiae can lead to bacteremia in elderly individuals with underlying conditions, primarily from cellulitis. Although rare, mediastinal abscesses can develop from anatomical anomalies, post-thoracic surgery, esophageal rupture, or inflammation in the oral cavity or neck. Aorto-esophageal fistula, a life-threatening condition causing severe bleeding, typically arises from thoracic aortic aneurysms with atherosclerosis. We present a case of recurrent Streptococcus dysgalactiae bacteremia complicated by mediastinal abscess and aorto-esophageal fistula in a patient undergoing treatment for gastric cancer. Initial imaging suggested lymph node metastasis, with a diagnosis of abscess only confirmed at autopsy. Although the exact etiology of the abscess was unclear, we highly suspect the recurrent Streptococcus dysgalactiae bacteremia contributed to its development via hematogenous spread. Autopsy also revealed progression of the mediastinal abscess into the esophagus and aorta, leading to the formation of a fistula, massive hemorrhage, and ultimately, the patient's death. While uncommon, a mediastinal abscess should be recognized as a potential cause of aorto-esophageal fistula.