Rapid Tests Diagnose Drug Resistant Tuberculosis

Three diverse diagnostic tests could each be used to detect drug resistance in tuberculosis (TB) patients in a quarter of the time taken by the current method.

Drug susceptibility tests are carried out in people with active TB in order to identify which drugs the causative agent Mycobacterium tuberculosis bacteria are sensitive or resistant to. This is particularly important for patients with extremely-drug-resistant TB (XDR-TB), who may have a short life expectancy if not treated properly.

Scientists at the University California, (San Diego, CA, USA) analyzed three new tests: pyrosequencing, a DNA sequencing technique; a commercial test that detects genetic mutations in the bacteria; and the microscopic observation drug susceptibility (MODS) test which screens samples under the microscope. The effectiveness of the tests was investigated in over 1,000 patients in India, Moldova, and South Africa.

The investigators performed the standard drug susceptibility tests, alongside the three novel tests and evaluated drug resistance to the following drugs: isoniazid, rifampin, moxifloxacin, ofloxacin, amikacin, capreomycin, and kanamycin. The results showed that the MODS test took 15 days to complete, the pyrosequencing took eight days to complete and the line probe assay (Hain Lifescience; Nehren, Germany) took five days. All three tests produced the same results as the standard testing, 95% to 98% of the time for almost all the drugs.

Antonino Catanzaro, MD, a professor of medicine and director of tuberculosis control at the University of California, San Diego, said, “Our findings suggest these three tests could provide a quicker way to identify patients who need alternative treatment regimens. This is very important and could potentially save lives as well as help to curb the rise of drug resistant TB. There are benefits and disadvantages to each test. For example, the MODS test, although the slowest of the three new tests we looked at, is much cheaper. It is important to have this range of options available so that TB treatment programs across the world can assess which method is right for them including consideration of the financial restrictions they work within.” The study was presented on September 8, 2013, at the European Respiratory Society's Annual Congress, held in Barcelona (Spain).

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