Recurrent Lelliottia amnigena Septic Arthritis in an Immunocompetent Child

Human infections secondary to Lelliottia amnigena are rare and have been reported almost exclusively in immunocompromised hosts or following penetrating trauma. We present the case of a previously healthy four-year-old girl who developed left knee septic arthritis caused by L. amnigena without a history of penetrating trauma. Her diagnosis was delayed by initially negative synovial fluid cultures, inconsistent organism nomenclature between laboratories, and a weakly positive Borrelia burgdorferi enzyme-linked immunosorbent assay (ELISA) that broadened the differential. Her symptoms resolved at the completion of her first treatment course. Approximately 18 months later, she re-presented with recurrent left knee infection due to L. amnigena. She was treated with surgical drainage followed by a three-month course of trimethoprim/sulfamethoxazole with complete resolution. This case highlights an unusual pathogen in pediatric septic arthritis and underscores the importance of considering extended or tailored antimicrobial therapy when managing rare organisms with poorly characterized virulence and relapse potential.