BackgroundDespite, Sri Lanka lies in the melioidosis endemic belt between 5°N and 10°N surrounded by countries known to have endemic melioidosis for many years, comparatively fewer cases of melioidosis infection have been reported in Sri Lanka. Melioidosis has a wide spectrum of clinical presentation, ranging from severe pneumonia to abscess formation in various organs. Isolated septic arthritis, which is a rare but well-recognized manifestation of melioidosis, could be the sole presenting problem in some patients with melioidosis.Case presentationWe report a middle aged diabetic female who has been on azathioprine for autoimmune hepatitis, presenting with pain and swelling of left hip joint. Investigations confirmed the clinical suspicion of septic arthritis, but all relevant microbiological investigations failed to isolate a causative organism. Due to the history of diabetes, possible immunosuppression with azathioprine, and failure to recognise the possible causative organism by initial investigations prompted us to investigate for melioidosis. Diagnosis of melioidosis was made by presence high titre of antibodies to melioidin antigen, and rapid response to appropriate treatment. The patient was treated with intravenous imipenem 1000 mg 6 hourly and oral cotrimoxazole (1920 mg 12 hourly) for 4 weeks followed by eradication therapy with cotrimoxazole and doxycycline.ConclusionGiven that melioidosis-induced septic arthritis share common features with septic arthritis due to other common pyogenic bacteria, differentiation of these two conditions is extremely difficult. Therefore, melioidosis needs to be considered as a possibility, when a patient with risk factors for melioidosis such as diabetes or immunosuppression presents with isolated septic arthritis. This case report has been presented to raise the awareness of an unusual presentation of melioidosis; isolated septic arthritis.