Tuberculosis is an infection that usually involves the lungs but can also affect other areas of the body. People can develop tuberculosis when exposed to someone with it, especially if the infected person is coughing. People exposed to tuberculosis do not always become sick. The tuberculosis bacteria can “hide out” in a person's body for many years—a situation called latent tuberculosis. Doctors can tell when patients have latent tuberculosis because they have positive tuberculosis skin tests but normal chest x-rays and no symptoms. Because latent tuberculosis can become active many years after exposure, doctors treat people with latent tuberculosis with antibiotics unless their age or medical history makes them at high risk for the side effects of treatment. The most common serious side effect of tuberculosis treatment is liver damage. Guidelines suggest three main treatment options for latent tuberculosis: 1) isoniazid for 6 to 9 months, 2) rifampin for 4 months, or 3) rifampin and pyrazinamide for 2 months. This last option is attractive because patients have to take drugs for only 2 months. Unfortunately, several reports of liver problems in people taking rifampin plus pyrazinamide have raised concerns about the safety of this treatment.