Abstract 
Mycobacterium szulgai (M. szulgai ) is an opportunistic and rare pathogen. Several risk factors play roles in the development of disease caused by this bacterium including immunodeficiency syndromes, previous Mycobacterium tuberculosis infection and smoking. We reported a case of M. szulgai respiratory infection in a 32-year-old male patient without any history of smoking, immunodeficiency syndromes or receiving immunosuppressive medications but the patient was severely deficient in vitamin D. Finally, the following treatment regimen was administered to the patient: isoniazid, rifampin, ethambutol, clarithromycin antimicrobial agents supplemented with vitamin B6 and vitamin D. The patient’s clinical condition was improved after 10 months of treatment. Vitamin D deficiency should be considered as a risk factor for M. szulgai pulmonary infection in immunocompetent people who are daily exposed to very little sunlight due to weather, occupational, or religious reasons.
Key Clinical Message: Closer attention should be paid to vitamin D status in patients with mycobacterial diseases.
Keywords : Mycobacterium szulgai , pulmonary infection, vitamin D deficiency, case report