The World Health Organization (WHO) estimates 11.4 million people worldwide are infected with both Mycobacterium tuberculosis (Mtb) and HIV. The primary cause of death in those infected with both microbes is from TB, not AIDS. In the United States, health experts estimate about two out of ten people who have TB are also infected with HIV. One of the first signs that a person is infected with HIV may be that he or she suddenly develops TB. This form of TB often occurs in areas outside the lungs, particularly when the person is in the later stages of AIDS. It is much more likely for people infected with Mtb and HIV to develop active TB than it is for someone that is infected only with Mtb. Fortunately, TB disease can be prevented and cured, even in people with HIV infection. People infected with both multidrug-resistant TB (MDR TB) and HIV appear to have a more rapid and deadly disease course than do those with MDR TB only. If no medicines are available, as many as eight out of ten people with both infections may die, often within months of diagnosis. Diagnosing TB in people with HIV infection is often difficult. They frequently have disease symptoms similar to those of TB and may not react to the standard TB skin test because their immune systems do not work properly. X-rays, sputum tests, and physical exams also may fail to show evidence of Mtb infection in people infected with HIV.