Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis bacteria. TB primarily targets the lungs but may affect any area of the body. It can be spread through the air from person to person through droplets of respiratory secretions such as sputum or aerosols released by coughing, sneezing, laughing, or breathing.
Most of those who become infected with M. tuberculosis manage to confine the mycobacteria to a few cells in their lungs, where they stay alive but in an inactive form. This latent TB infection does not make the person sick or infectious and, in most cases, it does not progress to active tuberculosis. However, some people - especially those with compromised immune systems - may progress directly from initial TB infection to active tuberculosis. People who have HIV are much more likely to become sick if they contract TB. A person who has latent TB and their immune system becomes weakened may then develop active TB. Another increasing concern is drug-resistant forms of TB that are resistant to the antibiotics typically prescribed to treat the disease.
TB is one of the world's deadliest diseases, although it is relatively uncommon in the U.S. Still, it is a large health issue among at-risk groups. Current guidelines call for targeted screening among such groups.
- People who have close contact with a person who has known or suspected TB disease
- People with weakened immune systems such as resulting from HIV infection, malnutrition, advanced age, or substance abuse including alcohol and drugs
- Immigrants from countries with a high rate of TB disease (many countries in Latin America, Africa, Asia, Eastern Europe, and Russia)
- Medically underserved people, such as those from a low-income environment
- Residents of long-term care facilities (such as nursing homes, mental health facilities, prisons, AIDS care facilities, and homeless shelters)
- People who live in unclean or crowded environments and/or without healthy food
- Health care workers who work in any of the above situations or with patients who are at increased risk
- Laboratorians who work with specimens that may contain TB or with TB cultures
The U.S. Centers for Disease Control and Prevention (CDC) recommend use of TB tests to identify people who will likely benefit from treatment, including those at increased risk for M. tuberculosis infection or for progression to active TB if they are infected. There are two types of tests that might be performed (see TB Screening Tests):
- Tuberculin skin test (TST) also called the Mantoux tuberculin skin test, the TST (or PPD for Purified Protein Derivative) is performed by injecting a small amount of fluid (called tuberculin) into the skin in the lower part of the arm. Following this test, you must return within 48 to 72 hours for a trained health care worker to look for a reaction.
- TB blood test: also known as IGRA (Interferon gamma release assay), requires a blood sample to be drawn.
Your health care provider will choose which TB test to use. Factors in selecting the test include the reason for testing, logistical considerations, prior vaccination with BCG, and test availability. Generally, it is recommended to be screened with either a TST or an IGRA, but not both.
Sources Used in Current Review
Mazurek GH et al. Updated Guidelines for Using Interferon Gamma Release Assays to Detect Mycobacterium tuberculosis Infection --- United States, 2010. Morbidity and Mortality Weekly Report. June 25, 2010 / 59(RR05);1-25. Available online at http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5905a1.htm?s_cid=rr5905a1_e through http://www.cdc.gov. Accessed October 2012.
Centers for Disease Control and Prevention. Tuberculosis (TB). Available online at http://www.cdc.gov/tb/. Accessed October 2012.
Centers for Disease Control and Prevention. TB: Testing & Diagnosis. Available online at http://www.cdc.gov/tb/topic/testing through http://www.cdc.gov. Accessed October 2012.
Hauck FR et al. Identification and Management of Latent Tuberculosis Infection. Am Fam Physician. 2009 May 15;79(10):879-886. Available online at http://www.aafp.org/afp/2009/0515/p879.html through http://www.aafp.org. Accessed October 2012.
U.S. Preventive Services Task Force. Screening for Tuberculosis Infection. Release date 1996. Available online at http://www.uspreventiveservicestaskforce.org/uspstf/uspstubr.htm through http://www.uspreventiveservicestaskforce.org. Accessed October 2012.
MayoClinic.com. Tuberculosis. Available online at http://www.mayoclinic.com/health/tuberculosis/DS00372 through http://www.mayoclinic.com. Accessed October 2012.