New CDC Guidelines Prefer Use of Blood Tests to Diagnose TB Infection in Certain Populations

The Centers for Disease Control and Prevention (CDC) has issued new guidelines on the detection of Mycobacterium tuberculosis infections, the causative agent of tuberculosis (TB).

In these guidelines, the CDC advises that Interferon Gamma Release Assay (IGRA) blood tests are now preferred over the 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-Guerin (BCG) as a vaccine or for cancer therapy. Typically the TST or IGRAs, such as QuantiFERON®-TB Gold (QFT), manufactured by Cellestis Limited, should be used as aids to diagnose infection with M. tuberculosis.

"In the U.S., up to 14 million Americans may be infected with TB bacteria and are at risk of developing full-blown, highly contagious TB. With these sobering numbers, complacency about TB's public health impact is not an option," said Antonino Catanzaro, MD, professor of medicine at the University of California San Diego, and non-executive independent director of Cellestis Limited. "These guidelines encapsulate the enormous body of clinical evidence on the performance of the QFT test and reflect the significant benefits this test is bringing to TB control worldwide."

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, 2010 (Vol. 59, No. RR-5) issue of the Morbidity & Mortality Weekly Report (MMWR). TST's drawbacks – which 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 – were evaluated by the CDC and factored into their recommendations.

Approximately one person dies of TB every 17 seconds. Each infected person represents a potential yet preventable future outbreak. Convenient and trustworthy testing for TB infection is vital in order to efficiently identify the appropriate persons for treatment and thereby prevent its spread.

The populations specified by the CDC in these guidelines, represent a majority of those being screened for TB infection. "With a specificity of more than 99 percent, QFT virtually eliminates false positive results and is simple to administer," said Tony Radford, chief executive officer of Cellestis Limited. "With more than 400 peer-reviewed, published clinical studies, QFT is a modern, scientifically–validated solution for reliable diagnosis of TB infection, and offers significant economic and public health advantages."

Specific highlights from the recommendations with regard to IGRAs include:

-- IGRAs are preferred over the TST for testing persons who have received BCG (as a vaccine or for cancer therapy).

-- IGRAs are preferred over the TST for diagnosing TB infection for persons from groups that historically have low rates of returning to have TSTs read.

-- IGRAs may be used in place of (not in addition to) TST in all situations in which CDC recommends testing, and is considered acceptable medical and public health practice.

-- IGRAs may be used in place of TST (without preference) to test recent contacts of persons with infectious tuberculosis.

-- IGRAs may be used in place of TST (without preference) for periodic screening to address occupational exposure to TB.

-- A TST is preferred for testing children aged <5 years. Use of an IGRA in conjunction with TST has been advocated by some experts to increase diagnostic sensitivity in this age group. Recommendations regarding use of IGRAs in children have also been published by the American Academy of Pediatrics.

Tuberculosis (TB) is a contagious disease caused by a bacterium called Mycobacterium tuberculosis. 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.

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. Convenient and trustworthy testing for TB infection is necessary in order to quickly identify the appropriate persons for treatment and thereby prevent its spread.

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