Unraveling the Uncommon: Salmonella agona Sacroiliitis in an Immunocompetent Adolescent – A Rare Musculoskeletal Manifestation

Abstract Septic sacroiliitis (SI) and its association with Salmonella agona in immunocompetent individuals is an atypical and exceptionally rare condition in clinical practice. This case report details a 16-year-old male who presented with acute right hip pain, high-grade fever, and difficulty bearing weight. S. agona was isolated from a computed tomography-guided biopsy of the sacroiliac joint and identified through molecular characterization (multi-locus sequence typing). The patient was successfully treated with intravenous third-generation cephalosporins and oral TMP-SMX over 8 weeks, leading to substantial clinical and functional improvement. This case underscores the importance of including rare pathogens like S. agona in the differential diagnosis of SI, especially when traditional risk factors such as trauma or immunosuppression are absent.