TUBERCULOSIS: New two-hour TB test

3 September 2010
A new, accurate, easy-to-use test can diagnose tuberculosis (TB) - including drug-resistant strains of the disease - in less than two hours. It has the potential to save thousands of lives in developing countries, where current tests are often unreliable, take weeks to process, or are simply unavailable. The Xpert MTB/RIF test detected TB in 98 percent of active cases, according to a study by the Foundation for Innovative New Diagnostics (FIND), a non-profit organization based in Switzerland. The test also correctly identified 98 percent of cases that were resistant to rifampin, a commonly used first-line TB drug. Resistance to rifampin indicates that a patient more than likely has multidrug-resistant (MDR)-TB, a growing global problem, particularly in countries with severe HIV epidemics. The usual way of diagnosing TB - a smear test - uses a microscope to check for the presence of TB bacterium in a sample of a patient's sputum. Although it is cheap and low-tech, the shortage of personnel trained to perform smear tests means patients often have to wait several days for a result. Smear tests also cannot identify patients with drug-resistant strains of the disease, and often fail to detect TB in patients co-infected with HIV, of which there are an estimated 1.37 million worldwide. Culture testing is much more accurate and can tell if the TB bacterium is resistant to various antibiotics, but it requires sophisticated laboratories and skilled technicians, and can take up to six weeks, by which time the patient may have infected many others and, in many cases, died. The new test - developed over five years by a public-private partnership between FIND, a California-based company called Cepheid Inc., and the University of Medicine and Dentistry of New Jersey in the US - uses polymerase-chain-reaction (PCR) technology to detect the DNA of the TB bacterium. After only two or three days' training, technicians participating in the study could insert a sample into a small cartridge and place it in an automated processor, which performed the test within two hours. The study, published in the New England Journal of Medicine on 1 September, involved 1,730 patients with suspected TB from Peru, Azerbaijan, South Africa and India, and compared the results of smear and culture testing with the results from Xpert MTB/RIF tests. Among patients who were smear-negative but culture positive, the new test detected TB in 72 percent of cases, a second test found 85 percent of cases, and a third caught 90 percent. The study only looked at using the new test in reference laboratories, and it is not certain that the findings could be replicated if the test were used in clinics. Cost could also be an obstacle. FIND has negotiated lower prices for public-sector programmes in low-income countries, but the cost will still be considerably more than for smear tests. Nevertheless, Dr Mario Raviglione, director of the World Health Organization (WHO) Stop TB Department, was upbeat about the new test's potential to save lives. "It is literally a revolutionary tool that, if implemented where it is needed, really ... [could] change the way we're doing TB care and control today," he told IRIN/PlusNews. WHO has funding from UNITAID, the international drug funding mechanism, to help countries implement the new tool if an advisory body recommends it. An expert committee is meeting in Geneva to review evidence from the FIND study and other research before making a recommendation by the end of September. "If they find that the evidence is good," Raviglione said, "then we may go public to tell the countries of the world to please start implementing this tool."