Zoonotic Streptococcus Equi Subspecies Epidemicus Bacteremia with Prosthetic Joint Injection and DVT in an Elderly Patient: a Case Report and Literature Review

Suwanee, GA

Introduction

Streptococcus equi subspecies zooepidemicus (SEZ) is a beta-hemolytic group C streptococcus commonly found in the upper respiratory tract of horses and other animals. Although SEZ is a frequent cause of equine “strangles,” human infection is exceptionally rare and associated with direct animal contact or consumption of unpasteurized animal products. Human SEZ infections have been reported to present with bacteremia, septic arthritis, endocarditis, or meningitis—particularly in immunocompromised individuals—but involvement of prosthetic joints is scarcely described in the literature. This case highlights an unusual zoonotic presentation of SEZ bacteremia in an elderly male with frequent equine exposure that was complicated by septic arthritis of a prosthetic knee and deep vein thrombosis (DVT), underscoring the importance of considering zoonotic pathogens in atypical musculoskeletal infections.

Methods

We report the clinical course of a 73-year-old male with Parkinson’s disease, a history of pulmonary embolism, and a prior left total knee arthroplasty who presented with acute fever, shaking chills, and progressive weakness. Initial laboratory evaluation included complete blood count and blood cultures. Microbiologic identification utilized matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry to confirm the organism. Imaging modalities, including Doppler ultrasound and computed tomography (CT) of the chest, abdomen, and pelvis, were employed to evaluate for potential sources of infection and complications. Management included broad-spectrum empirical antimicrobial therapy followed by targeted intravenous and oral antibiotics. A literature review was also conducted to contextualize this presentation compared to other reported cases of SEZ infection in humans.

Results

The patient presented with a fever of 103.3 °F, hypotension, leukocytosis with neutrophil predominance, and elevated inflammatory markers. Blood cultures from four separate bottles consistently grew S. equi subspecies zooepidemicus. He reported frequent exposure to horses, correlating with a likely zoonotic transmission. Physical exam and imaging revealed symptoms of septic arthritis in the prosthetic left knee and an acute right lower-extremity DVT identified on Doppler ultrasound. Systemic CT imaging demonstrated diffuse esophageal and rectal wall thickening, though these findings did not clarify the primary infectious source. The patient received an initial course of piperacillin-tazobactam for three days, followed by six weeks of intravenous ceftriaxone, then transitioned to oral amoxicillin-clavulanate for six months, which was later extended based on clinical progress and inflammatory marker trends. Over time, he tolerated oral intake with resolution of systemic signs of infection.

Discussion

This case represents a rare instance of SEZ bacteremia leading to prosthetic joint infection and DVT in an elderly patient with significant equine exposure. Human infection with SEZ is infrequent and often occurs in those with direct animal contact or other risk factors. The identification of SEZ as a cause of prosthetic joint infection is particularly unusual and highlights the need for thorough history-taking in patients with atypical infections and potential zoonotic exposures. Prompt recognition is critical to managing these rare infections, especially given the potential for systemic complications such as septic arthritis and thrombotic events. Continued surveillance and reporting of such cases will help better characterize the spectrum of disease and inform optimal diagnostic and therapeutic strategies.