Better and faster: Distinguishing non-TB pulmonary disease from TB

A diagnostic kit shows new promise for distinguishing between tuberculosis (TB) and its infections from disease caused by related mycobacteria family, which mimic TB and other lung disease in symptoms but require distinctly different clinical treatments.

The bacterium that causes TB, mycobacteria tuberculosis, comes from a larger family of mycobacteria, certain strains of which can cause lung disease. The most common pathogenic nontubercular mycobacteria are known together as Mycobacterium avium complex, or MAC. Distinguishing MAC-related pulmonary disease (MAC-PD) from TB is difficult, and can take eight weeks or more. Complicating matters, MAC bacteria are ubiquitous in the environment, and a positive culture may mean nothing more than specimen contamination.

Now, researchers have shown in a multi-center study that differentiating MAC-PD from TB can be accomplished in just a few hours using an assay that can identify antibodies specific to MAC.

The research was published in the first issue for April of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.

MAC is responsible for a growing proportion of pulmonary disease, but how much is unclear. “There are more cases being reported,” said Dr. Alvin Teirstein, professor of medicine at Mount Sinai School of Medicine. “We are not sure where it was hiding 25 years ago, but there appears to be a growing epidemic over the last 20 years.”

Up to now, distinguishing between MAC and TB largely relied on a suite of clinical signs and obtaining repeatedly positive sputum cultures—a process that was both unwieldy and often unreliable. “About 20 percent of the time the physician might make the wrong determination,” said Dr. Teirstein.