Revolutionary new test to combat TB

Lawrence Altman

Lawrence Altman

A new test that can detect multiple-drug-resistant tuberculosis in two days instead of the standard two to three months promises to help significantly improve treatment and prevent the spread of the airborne infection, the World Health Organisation announced this week.

Multiple-drug-resistant TB, or MDR-TB, is a growing public health problem in the world. Five percent of new TB cases are resistant to first-line drugs. That is 450000 of the nine million new TB cases that are detected each year, the WHO says.

In the United States, the prevalence of drug-resistant tuberculosis among foreign-born TB patients has been about 1,5percent, roughly three times the percentage among American-born patients with TB.

"The new test is revolutionary," said Dr Mario Raviglione, the WHO's director of tuberculosis control, because "it changes completely the way we will be dealing with MDR-TB".

Detecting cases rapidly and accurately is a major source of delay in tuberculosis control. In most developing countries, cases cannot be detected easily or at all, leading to lags in starting proper treatment that can lead to a patient's death and the further spread of resistant strains.

The new test was described to journalists by telephone on Monday by officials of the WHO and three other international health groups - the Stop TB Partnership, Unitaid and the Foundation for Innovative New Diagnostics, or Find.

The TB test, called a line probe assay, costs less than R56 and detects mutations in bacterial DNA linked to drug resistance.

It is based on the same laboratory methods that scientists have used to determine parentage and detect certain genetic diseases, said Dr Richard O'Brien, an official of Find.

The test could have been developed five years ago if there had been greater funds and demand. Raviglione of WHO said it took widespread publicity about an outbreak in South Africa of XDR-TB, a shorthand for extensively-drug-resistant TB, to demonstrate the urgency and duty to bring sophisticated technology to poor countries.

The WHO, a UN agency, estimates that worldwide only two percent of drug-resistant cases are now being detected and treated appropriately, mainly because of a breakdown in the global programme that is supposed to keep the disease under control.

Drug-resistant TB, like drug-sensitive TB, can be transmitted by an infected individual in droplets through coughing, sneezing, singing and other activities.

It may require two years of treatment with drugs that are much more costly than the first-line regimen. Technically difficult surgery may also be required.

Health officials have sounded alarm bells because they believe that TB could reach the point where most new cases in some countries are resistant to many drugs without efforts like the new laboratory test to help stop the spread of the disease.

A concern is the potential for outbreaks of MDR-TB to evolve into those of the even deadlier XDR-TB.

The TB test is performed in a series of steps. Technicians begin by extracting DNA directly from a sputum specimen and then use amplifying techniques to produce large numbers of copies of the DNA.

Technicians go on to determine the presence of certain genetic mutations that are linked to resistance with the most important anti-TB drugs, isoniazid and rifampin.

Raviglione and other officials urged use of the test everywhere, particularly in poor countries where HIV is also epidemic. HIV, the Aids virus, increases the risk of tuberculosis. Versions of the test are licensed in a number of European countries, Canada and Japan, but not in the US, the teleconference speakers said.

Technicians need training in performing the test because they are at considerable risk of becoming infected. Also, contamination can invalidate test findings.

Researchers have documented the test's accuracy in South Africa, where government officials were expected to recommend its widespread use.

The test is also being used in Lesotho and Latvia and is expected to be used in Ethiopia later this year. Thirteen additional countries are expected to begin using it by 2011 under support from Unitaid.

Technicians who had no prior experience learned how to do the sophisticated molecular test in a week, and experience has shown that high-quality laboratories in the poorest countries can obtain test results comparable to those in richer countries, O'Brien said. - New York Times