National Health and Nutrition Examination Survey (Nhanes)

The Centers for Disease Control and Prevention (CDC), Division of Tuberculosis (TB) Elimination, is responsible for the TB skin-testing component of NHANES. The objective is to determine the prevalence of TB infection in the U.S. population. All sample persons (SPs) aged 6 years or older are offered testing for infection with the bacterium that causes TB. TB is a disease caused by a germ called Mycobacterium tuberculosis that is spread from person to person through the air. TB usually affects the lungs, but it can also affect other parts of the body, such as the brain, the kidneys, or the spine. When a person with infectious TB coughs or sneezes, droplet nuclei containing M. tuberculosis are expelled into the air. If another person inhales air containing these droplet nuclei, he or she may become infected. However, not everyone infected with TB bacteria becomes sick. As a result, two TB-related conditions exist: latent TB infection and active TB disease. Persons with latent TB infection do not feel sick and do not have any symptoms. They are infected with M. tuberculosis, but do not have active TB disease. The only sign of TB infection is a positive reaction to the tuberculin skin test or TB blood test. Persons with latent TB infection are not infectious and cannot spread TB infection to others. Overall, about 5-10 percent of infected persons will develop active TB disease at some time in their lives. About half of those people who develop active TB will do so within the first 2 years of infection. For persons whose immune systems are weak, especially those with HIV infection, the risk of developing active TB disease is considerably higher than for persons with normal immune systems. People exposed to someone with active untreated infectious TB for prolonged periods are most likely to acquire the disease. Casual brief contact is unlikely to result in TB transmission. Tuberculin skin tests and blood tests, allow clinicians to look for TB infection in household or workplace contacts of people with active disease. Treatment to prevent active TB disease is recommended for some persons whose skin test and clinical evaluation indicate TB infection, but who do not have TB disease, and who do not have contraindications to the medications.