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.

Furthermore, even though initial diagnosis is uncertain, patients whose sputum is positive for acid-fast bacilli are often immediately isolated and sometimes started on a regimen of anti-TB drugs. Isolating non-TB patients and beginning inappropriate treatment regimens not only drains resources that could be used to treat infectious TB, it is a burden and risk to the patient as well. In contrast to TB, MAC is not contagious and sometimes requires no treatment.

“Diagnosis of pulmonary disease due to MAC is complicated and time-consuming,” wrote Seigo Kitada, lead researcher on the study. “In the context of infection control it is particularly important to distinguish between MAC-PD and pulmonary TB.”

To test the efficacy of the immunoassay kit, the researchers acquired specimens from six centers between June 2003 and December 2005. The samples came from 70 patients with MAC-PD; 18 with MAC contamination, 36 with pulmonary TB, 45 with other lung disease and 76 from healthy patients.

They found that found that serum antibody levels to the MAC-specific antigen were higher in patients with MAC pulmonary disease as compared to those with other respiratory diseases, including tuberculosis. The sensitivity and specificity of the serologic test were 84.3% and 100%, respectively. Equally important, the test, took only hours as opposed to the four to eight weeks it takes to determine conventional culture results.

While Dr. Tierstein points out that to be validated, the kit must perform well with different populations and in different locations, as MAC strains can vary from place to place, this is the first multi-center demonstration of the efficacy of such a kit, raising the hope that it may solve the problem of distinguishing MAC-PD from TB and represents a critical step in increasing the accuracy and efficiency in treating patients with MAC-PD and TB.

Source: American Thoracic Society

Related stories:

Looking for the Founatain of Youth? Cut your calories, research suggests
Want to slow the signs of aging and live longer? New Saint Louis University research suggests cutting back on calories could be a promising strategy.
Blood vessel inhibitor shows promise against metastatic thyroid cancer
Thyroid cancer that has spread to distant sites has a poor prognosis, but an experimental drug that inhibits tumor blood vessel formation can slow disease progression in some patients, a research team led by investigators from The University of Texas M. D. Anderson Cancer Center reports in the July 3rd edition of The New England Journal of Medicine.
Disclosure of organ transplant risks: A question of when, not if
University of Pennsylvania School of Medicine physicians and bioethicists are calling for a new, more standardized way for patients in need of organ transplants to be informed of the risks they face. If adopted, their policy recommendations could promote greater equity in how organs are allocated while restricting patients' abilities to "cherry-pick" the best organs.
Smoking out the mediators of airway damage caused by pollutants
New insight into how pollution and cigarette smoke damage airways has been provided by Pierangelo Geppetti and colleagues, at the University of Florence, Italy, who studied the effects of such chemicals on guinea pig airways. As discussed, in an accompanying commentary, by Sidney Simon and Wolfgang Liedtke, at Duke University Medical Center, it is hoped that this information will help in the development of therapeutics to combat the effects of pollutants and perhaps help individuals with smoke-related diseases such as chronic obstructive pulmonary disease and chronic asthma.
Primary care visits reduce hospital utilization among Medicare beneficiaries at the end of life
Researchers from Boston University School of Medicine (BUSM) have found that primary care visits reduce hospital utilization among Medicare beneficiaries at the end of life. The recently published study appears in the Journal of General Internal Medicine.
Brief, intense exercise benefits the heart
Short bursts of high intensity sprints -- known to benefit muscle and improve exercise performance—can improve the function and structure of blood vessels, in particular arteries that deliver blood to our muscles and heart, according to new research from McMaster University.
Gene therapy slows progression of Batten Disease
Gene therapy that helps defective brain cells get rid of "garbage" appears both safe and effective at slowing down Batten disease, according to promising findings from NewYork-Presbyterian Hospital/Weill Cornell Medical Center.
Researchers find common gene disorder doubles risk of lung cancer, even among nonsmokers
Mayo Clinic researchers have found that carrying a common genetic disorder doubles the risk of developing lung cancer in smokers and nonsmokers. The study is published in the May 26 issue of the Archives of Internal Medicine, a journal published by the American Medical Association.

News discussion:

Medicine & Health news