New test can diagnose tuberculosis in under 2 hours

By Kate Kelland, Reuters

Posted at Sep 03 2010 10:14 AM | Updated as of Sep 03 2010 06:20 PM

LONDON - A new molecular test for tuberculosis made by Cepheid can diagnose TB and detect a drug-resistant form of it far more easily and rapidly than other tests currently available, scientists said on Wednesday.

In a study in the New England Journal of Medicine (NEJM), researchers said that when used on 1,730 patients with suspected TB and suspected drug-resistant TB, the Xpert MTB/RIF test successfully identified 98% of all cases.

It also identified 98% of patients with a form of TB resistant to rifampin, or rifampicin -- one of the most powerful TB drugs -- and achieved these results in less than two hours.

Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases described the test findings as "impressive" in terms of speed, accuracy and sensitivity.

"Within two hours, you can not only have a diagnosis, but you can also have a good idea of the range of drugs you can use," he told Reuters, adding that such capabilities were "unheard of" with current testing methods.

Doctors say current diagnostic testing for TB -- which involves microscopy in labs with trained experts and can take weeks -- has barely been improved in the last 125 years.

Tests for drug-resistant TB can take months and are notoriously insensitive, so new, more accurate tools to rapidly diagnose TB and its drug-resistant forms are urgently needed.

"We're very pleased with the outcome," said Mark Perkins, chief scientific officer at the Geneva-based non-profit organization the Foundation for Innovative New Diagnostics (FIND), which worked on the study.

TB afflicts mostly the poor in developing regions such as sub-Saharan Africa, India and China, but also occurs in poor regions of developed nations and is common in patients with the HIV virus that causes AIDS. It is among the world's top 10 leading causes of death and killed 1.8 million people worldwide in 2008, or one person every 20 seconds.


Perkins said his team had since followed up on this initial study and carried out further "demonstration trials" in six countries to see how the test works in real-life settings.

He said initial signs from these trials, which involved nearly 7,000 patients but have yet to be published or peer-reviewed, suggest the test is just as effective at detecting TB in real patients on the ground.

In a commentary about the NEJM study, Peter Small, who runs the TB program at the Bill & Melinda Gates Foundation global aid group, said he was encouraged by the results but concerned that the potential high cost of such a sophisticated test might limit its use around the world.

"Critical to a rapid scale-up of the test will be...whether its use improves outcomes for patients in a cost-effective manner," he wrote.

Perkins said FIND had already negotiated concessionary prices with Cepheid which would apply in developing countries which decide they want to use the test.

The machine and computer to analyze the tests cost around $17,500, and the negotiated price of the test kits for poorer countries will be based on the cost of manufacture plus a small margin, he said. He was not able to give a precise figure.

"Our goal is to make...tests as inexpensive as possible. This one happens to be quite sophisticated and quite difficult to make inexpensive. But it is like any other public good -- it will obviously have a big impact, and it obviously costs money."