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Experimental TB Test Gives Results in an Hour

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A new TB test has been developed that can tell doctors within one hour whether someone has tuberculosis. The test is in the experimental stages, but scientists say it has the potential to make a big difference in developing countries hit hard by TB. TB is a potentially deadly disease that strikes 10 million people each year. Two million of them die of the disease, according to experts. There are antibiotics to treat TB, but it can take up to three weeks to get a diagnosis, which delays treatment. The test that is often used in resource-poor countries is the Ziehl-Neelsen, or ZN, test. Developed in the 1880s, it is an 11-step process that begins when technicians put a sample of sputum on a microscope slide, then dye and rinse it multiple times. That alone can take several hours. In addition, it is often difficult to definitively detect the presence of the bacterium under the microscope. Meanwhile, the same sputum sample may be sent away to grow the TB pathogen in a dish. But mycobacterium grows slowly, taking as many as three weeks to yield a result. New test, quick results However, an experimental TB test has the potential to show clinicians what they need to know within one hour. Carolyn Bertozzi, a biological chemist at Stanford University in California, helped develop the rapid TB sputum test, which she said fills a treatment void in developing countries, where patients often disappear before they are diagnosed. "So, it's a real public health problem to not have an accurate test that, first of all, is more specific for TB, will tell you whether the TB are alive, and can be performed in a period of time where you can keep somebody in the clinic so you can act on the diagnosis while they are still there," Bertozzi said. How it works The rapid test uses sugar molecules found in the cell walls of the TB bacteria. Investigators tag modified versions of the sugar molecule with a fluorescent dye, which the live pathogens take up and integrate into their cell walls. Under the microscope, only the live mycobacteria, which cause tuberculosis, glow green. The test also could be used to check sputum samples to see whether someone being treated for TB is responding to the antibiotics, Bertozzi said. There's still more work to be done before the test becomes a reality. For now, Bertozzi sees it as a way to confirm a diagnosis using a microscope for a first-pass look for the TB microorganism. "I'm excited about it because it is so simple,” she said. “It is low-tech, but it kind of fulfills a niche in technology that doesn't exist right now in the world of either TB basic science or TB diagnosis." Field trials of the experimental test began in June in South Africa. A number of charitable organizations, including the Gates Foundation, have shown an interest. The work is being presented this week at the annual meeting of the American Chemical Society in Philadelphia, Pennsylvania, the world's largest scientific society.

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