New TB machine cuts six-week test to two hours

Dec 8th, 2010 5:26 PM UTC
By ONE Partners

David Bryden from the Center for Global Health Policy talks about the Xpert MTB/Rif test, a revolutionary technology that can diagnose whether a patient has TB in less than two hours.

Today is a day that will be long-remembered in the global battle to fight HIV/AIDS and tuberculosis (TB). After years of struggling with outdated technology, there is finally a new method for rapidly diagnosing TB, including TB in persons with HIV (which has special challenges) and drug-resistant tuberculosis.

Tuberculosis is an airborne, bacterial infection that is the single biggest killer of people living with HIV/AIDS.

Ever gotten a rapid HIV test? What would it be like if you had to wait as much as six weeks to get the result instead of minutes?

That’s often been the case for people living with HIV who are suspected of having TB. The most common way of diagnosing TB in developing countries is to look at the sputum under a microscope, but this method detects only about 20 percent of TB in people with HIV/AIDS and less than half of TB cases overall. It is not useful at all for detecting TB in children or in detecting drug resistant tuberculosis. A second method is to use solid or liquid culture, but this can take several weeks and requires sophisticated bio-safety procedures.

A lot can go wrong during this time lag — a patient could die for lack of proper treatment or infect others, including other patients in the HIV clinic or their own children, with TB.

In fact, TB in children is a much larger problem than people realize, and children who are infected develop the full-blown disease much faster than adults. TB-positive women are twice as likely to give birth to a premature or low birth-weight baby and four times more likely to die during childbirth.

These are some of the reasons why HIV/AIDS advocates are celebrating WHO approval of a new test for TB, called the Xpert MTB/Rif test, developed with assistance from the US government and the Bill and Melinda Gates Foundation.

Instead of taking weeks to diagnose a patient, this test can do it in less than two hours! It can also tell whether the TB is of the drug-resistant variety so the patient can get the right kind of medication.

Persons living with HIV are at high risk of dying from the disease, and once a person who is HIV-positive is diagnosed with TB, they are supposed to be put on a fast track to get antiretroviral treatment. When TB is diagnosed and treated, the patient quickly becomes non-infectious.

But there are some remaining challenges. The test is done with a machine about the size of an espresso coffee maker, which, outside of wealthy countries, costs $17,000 (based on a significant discount provided by the manufacturer, Cepheid).

The machine analyzes a sputum sample in a specially designed cartridge. These cartridges will initially sell for a discounted price of $16.86 and then $10.72 by 2014, when large-scale purchasing should lead to economies of scale. This makes it a very costly test for developing countries.

Unfortunately, according to the Treatment Action Group, Cepheid has not moved quickly enough to submit the test for approval for use in the US, which would help boost economies of scale and make this new tool available to patients with suspected TB in the US.

However, even at this price, the test compares well with other methods. An analysis by WHO showed that the cost of the new test will be similar to that of the conventional culture method. The test multiplies by three times the ability to detect multidrug- resistant TB. Experts are also looking into ways the machine could be used to diagnose TB in children.

PEPFAR wants to immediately implement use of the new test, and USAID says it will actively promote it. The approval of the test gives added urgency to recent appeals to the Obama Administration to propose major funding boosts for HIV/AIDS and TB in its FY 2012 budget, which is now being prepared.

-David Bryden, senior program policy officer, Center for Global Health Policy

TAGS: ONE, Policy News, Technology, Tuberculosis