We present a 23-year-old woman on immunosuppressive therapy with polyarticular, culture-negative septic arthritis. She underwent irrigation and debridement with empiric antibiotic therapy but had recurrence of septic arthritis despite treatment. Polymerase chain reaction testing eventually identified Ureaplasma as the causative organism. She was successfully treated with an extended course of organism-specific antibiotics.
More patients are being treated with immune modulating therapies. Immunosuppressed patients are at risk for atypical infections and may have different presentations than immunocompetent patients. Newer diagnostic modalities can help identify causative organisms and direct treatment in the case of negative cultures.