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colored x-ray of lung with TB nodule
Colored x-ray of lung with TB nodule
 

Novel molecular tests are gaining popularity as a rapid way to detect genetic mutations that render tuberculosis impervious to drug treatment. Yet, how well these new tests gauge the risk of actual drug failure and patient death has remained unclear.

Now, research led by HMS scientists shows that when it comes to predicting response to treatment and risk of dying, molecular tests that detect resistance to a class of tuberculosis drugs known as fluoroquinolones may be as good as, and even superior to, traditional drug-sensitivity tests conducted in lab cultures. The study was published August 3 in Clinical Infectious Diseases.

Traditional drug-sensitivity tests can take up to eight weeks to yield results. By comparison, point-of-care molecular tests provide results within hours, expediting treatment decisions.

Past research has indicated, however, that molecular tests may fail to detect resistance mutations in more than 30 percent of strains insensitive to the drug moxifloxacin. This failure rate has fueled anxiety about their reliability as resistance detectors.

“Culture-based testing is still considered the gold standard for diagnosing TB resistance,” says Maha Farhat, an HMS assistant professor in the Department of Biomedical Informatics and lead author of the study. “However, our results should provide reassuring evidence that molecular tests are just as reliable, if not better, in predicting overall treatment outcome as a result of such resistance-causing gene alterations in patients who fail treatment with fluoroquinolones.”

The researchers caution that their study involved only 171 patients and that further research is needed to reveal the predictive accuracy of molecular versus standard lab tests in other forms of drug-resistant tuberculosis.

The investigators add, however, that the data provide compelling evidence that molecular tests could become a mainstay in informing drug choice and predicting the clinical course of a patient’s infection.

“Widespread implementation of molecular tests to guide regimen development is critical to stemming transmission of, and illness and death due to, drug-resistant forms of tuberculosis,” says Carole Mitnick, an HMS associate professor in the Department of Global Health and Social Medicine and the study’s senior investigator.

Image: BSIP/Photo Researchers

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