Successful treatment of Mycobacterium terrae complex infection of the knee

Mycobacterium terrae is an unusual, ubiquitous organism that can cause clinical disease in both immunocompetent and immunocompromised hosts and can be difficult to diagnose and treat. We report a case of a 61-year-old man with a septic knee whose arthroscopy cultures grew M. terrae. The patient was successfully treated using a 6-month regimen of clarithromycin and sulfamethoxazole. Mycobacterium terrae should be considered in the differential diagnoses for monoarticular swelling and pain of unknown etiology, especially in the setting of initially negative routine microbiological cultures.