CDC Issues New Guidelines for TB Testing

The U.S. Centers for Disease Control and Prevention estimates that between 9 and 14 million Americans are tuberculosis (TB)-infected and asymptomatic -- with three-quarters remaining undiagnosed -- and at risk of progressing to a highly contagious form of TB disease. On Friday, CDC issued new and important guidelines on the detection of Mycobacterium tuberculosis infections, the causative agent of TB. In the guidelines, the agency advises that Interferon Gamma Release Assay (IGRA) blood tests are now preferred over the 100+-year-old tuberculin skin test (TST) for diagnosing TB infection in certain populations, including people who typically do not return for the necessary reading of TST results, and those who have received Bacille Calmette-Guérin (BCG) as a vaccine or for cancer therapy.

The CDC report, "Updated Guidelines for Using Interferon Gamma Release Assays to Detect Mycobacterium tuberculosis Infection -- United States, 2010," along with a companion implementation guide, appears in the June 25 issue of CDC's Morbidity & Mortality Weekly Report (MMWR, Volume 59, No. RR-5). In making its recommendations, CDC factored in TST's drawbacks, which its says include a higher risk for false positives, especially in people who have been BCG-vaccinated; irritating TB-extract that must be injected under the skin; and the need for a second doctor's visit.

According to the World Health Organization, about one person dies of TB every 17 seconds, causing nearly 2 million deaths annually. TB continues to be a contagious scourge in developing countries, and with the world shrinking rapidly due to global migration, it is a major public health threat in developed nations as well, including the United States. Each infected person represents a potential yet preventable future outbreak.

TB bacteria usually attack the lungs, but can affect any part of the body such as the kidney, spine, and brain. If not treated properly, TB can be fatal. TB bacteria is spread through the air when a person with TB disease of the lungs or throat coughs, sneezes, speaks, or sings, which may lead people in close proximity to become infected.

The populations specified by the new CDC guidelines represent a majority of those being screened for TB infection. Better, more reliable testing for TB infection is vital in order to efficiently identify the appropriate persons for treatment and thereby prevent its spread, the agency said.

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