A Rare Case of Streptococcus equi Infection: A Report and Brief Review of the Literature.

We present a rare case of Streptococcus (S.) equi subspecies zooepidemicus (SEZ) bacteremia in a 73-year-old male with a history of Parkinson's disease, pulmonary embolism, and recent left knee total arthroplasty who developed fever and sepsis complicated by septic arthritis of a prosthetic knee and deep vein thrombosis (DVT). Blood cultures grew S. equi in four out of four bottles, and history revealed frequent horse exposure, suggesting zoonotic transmission with hematogenous seeding of the prosthetic joint. The diagnosis was further challenged by systemic computed tomography (CT) abnormalities and the concurrent DVT, which initially obscured the infectious source. The patient was treated with three days of piperacillin-tazobactam before de-escalation to intravenous ceftriaxone for six weeks, followed by 6 months of oral amoxicillin-clavulanate, which was then extended for an additional 12 months based on clinical response. SEZ causing prosthetic joint infection is exceptionally rare, and this case underscores the importance of recognizing zoonotic pathogens as potential causes of hematogenous prosthetic joint infections, particularly in immunocompromised hosts.