This illustration depicts a three-dimensional (3D) computer-generated image of a cluster of rod-shaped drug-resistant Mycobacterium tuberculosis bacteria, the pathogen responsible for causing the disease tuberculosis (TB). The artistic recreation was based upon scanning electron micrographic imagery. TB is among the most common infectious diseases and a frequent cause of death worldwide. TB is spread most commonly through the air. M. tuberculosis can affect any part of the body, but disease is found most often in the lungs. In most cases, TB is treatable and curable with the available first-line TB drugs; however, in some cases, M. tuberculosis can be resistant to one or more of these drugs. Drug-resistant TB is more challenging to treat ? it can be complex and requires more time and more expensive drugs that often have more side effects. Extensively Drug-Resistant TB (XDR TB) is resistant to most TB drugs; therefore, patients are left with treatment options that are much less effective. The major factors driving TB drug resistance are incomplete or wrong treatment, short drug supply, and lack of new drugs. In the United States most drug-resistant TB is found among persons born outside of the country.