There are more than 70 species of mycobacteria, rod-shaped bacteria with waxy outer coats that can be found throughout the world. Tuberculosis and leprosy (Hansen's disease) are the best known mycobacterial diseases. People may also be infected by any of a group of mycobacterial species collectively called non-tuberculous mycobacteria. While tuberculosis and leprosy are most common in resource-limited countries, non-tuberculous mycobacterial infections occur worldwide.