According to the U.S. Centers for Disease Control and Prevention (CDC), 12,904 cases of tuberculosis were reported in the U.S. in 2008--the lowest number on record. However, tuberculosis (TB) remains a major public health threat globally. TB infections can be latent or active. With latent TB, the bacteria are inactive and cause no symptoms; latent TB is not contagious. With active TB, the causative bacteria--Mycobacterium tuberculosis--are actively multiplying causing a symptomatic and contagious illness.