Geoff Watts An instrument developed in the US after the country’s anthrax contaminated letters scare of 2001 has now been endorsed by the World Health Organization as a more effective means of testing for tuberculosis.
Manufactured by the Californian company Cepheid, the Xpert MTB/RIF uses a disposable cartridge containing all the reagents required to perform the test. Results are available in about 90 minutes.
Sputum smear microscopy, the method commonly used for detecting tuberculosis, was developed 125 years ago. It misses many cases, especially in children and people who are HIV positive. The diagnosis of drug resistant tuberculosis relies on bacterial culture and drug susceptibility testing. These findings are not available for weeks or even months during which time a drug resistant strain can continue to spread.
The new test is fully automated, poses few biosafety hazards, can be operated in a non-specialist laboratory, and detects the presence of rifampicin drug resistance, an indicator of multiple drug resistance. Patients can be offered the appropriate treatment immediately.
Demonstrated this week at press conferences held in London and Geneva, journalists were able to see for themselves how straightforward the instrument is to use.
The operator first scans the bar code on a small lidded cartridge, a few centimetres square. The addition to the sputum sample of a prepared solution renders it non-infectious within 15 minutes. Using a pipette, 2 mL of this mixture are put into the cartridge which, after closing its lid, is slipped into the instrument. The results are displayed on a laptop computer.
Giorgio Roscigno, chief executive of the Foundation for Innovative New Diagnostics (FIND), the not-for-profit organisation that helped to develop its application to tuberculosis, said, “By changing the cartridges you could also use this instrument for other diseases.”
Explaining WHO’s decision to endorse the instrument Karin Weyer, of its Stop TB department, pointed to the accumulated data. “An expert group reviewed the evidence from around 12 000 patients evaluated in a variety of settings,” she said. “We are now recommending that we move as quickly as possible to provide policy guidance and a road map to countries to get this test working in the field.”
Multiple drug resistance poses a severe challenge to national tuberculosis programmes according to a recent editorial in the New England Journal of Medicine (2010;363:1070-1). “Globally,” say the authors, “fewer than two per cent of the estimated cases of multi-drug resistant disease are reported to the WHO and managed according to international guidelines.”
The new instrument costs $17 000 (£10 800; €12 900) and can perform 16-20 tests in eight hours. Each test costs $16.86, but will drop to $10.72 by 2014 if uptake proceeds as intended. South Africa and India are among countries that have plans to use the system, and many non-governmental bodies active in fighting tuberculosis have also expressed interest or said they will promote it.
http://www.bmj.com/content/341/bmj.c7132.full
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