New test detects TB faster, with more accuracy than current diagnostics, study says

Sep 3 2010

A new molecular test for tuberculosis can diagnose the disease and detect a drug-resistant form of it in less than two hours and more accurately than current tests, according to the findings of a study published online in the New England Journal of Medicine on Wednesday, Reuters reports (Kelland, 9/1).

As described by the authors of the NEJM study, between July 2008 and March 2009 at trial sites in Lima, Peru; Baku, Azerbaijan; Cape Town and Durban, South Africa; and Mumbai, India, "We enrolled consecutive adults with symptoms suggestive of pulmonary tuberculosis or multidrug-resistant tuberculosis who were able to provide three sputum samples." The authors add, "All patients were enrolled from populations that were selected for diversity in the prevalence of tuberculosis, HIV coinfection, and multidrug resistance" (Boehme et al., 9/1).

In total, the researchers tested the sputum of "1,730 patients with suspected TB," Reuters writes (9/1). The test, known as Xpert MTB/RIF, identified TB in 98 percent of active cases and also detected 98 percent of TB cases that were resistant to "rifampicin, a first-line drug for TB," Nature News reports (Mandavilli, 9/1).

Currently, the most commonly used test, which was developed 125 years ago, "can take days to perform because of backlogs of [smear] specimens and the need for trained personnel and is only 50% accurate," the Los Angeles Times notes. "Moreover, it doesn't work in patients who are HIV-positive" (Maugh, 9/1). According to the study findings, the MTB/RIF test detected 93.9% of TB cases in HIV-postitive patients "as compared with 98.4% in HIV-negative patients" (Boehme et al., 9/1).

The Xpert MTB/RIF test, developed by Cepheid Inc., uses the GeneXpert, an automated processor, to analyze samples. "The test itself uses what is known as PCR technology to make many copies of any bacterial DNA in the specimen for analysis. ... Interestingly, the technology was originally created for the U.S. Post Office to help postal workers check for anthrax contamination in mail, and has been adapted to diagnose TB," the Los Angeles Times notes.

"The new test, which can be performed by technicians with only limited training, could prove highly valuable ... The World Health Organization is expected to decide by the end of this month whether to recommend use of the new test by its member countries. 'These results suggest that it has the potential to revolutionize TB care, and WHO will treat it as a top priority,' the agency said in a statement" (9/1).

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said the test's speed, accuracy and sensitivity were "impressive," Reuters reports. "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 said (9/1).

However, the test has its limits, Nature News writes. "The test has so far been used only in relatively well-equipped labs. It has not yet been trialled in places with a lot of dust or an unreliable power supply, both of which could cause problems with the PCR equipment. ... Another key issue is price, which is still being negotiated ... Even with a high-volume discount, the cost per test is likely to be more than the roughly US$8 for multiple conventional tests - smear plus culture, or multiple rounds of smear," according to the news service (9/1).

Study author Mark Perkins, the chief scientific officer at the non-profit organisation the Foundation for Innovative New Diagnostics (FIND), "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," Reuters writes. Initial reports from the new trials, which include almost 7,000 patients, have shown the test as just as effective in diagnosing TB in other settings, he said. Those findings have not yet been published (9/1).

According to a FIND press release, the test was developed along with "its partners Cepheid and the University of Medicine and Dentistry of New Jersey" and "supported by the U.S. National Institute of Allergy and Infectious Diseases (NIAID), Cepheid and the Bill & Melinda Gates Foundation."

FIND CEO Giorgio Roscigno said, "Once WHO has issued a recommendation on the use of the test, FIND will work with international partners and national health programmes to accelerate global access to this potentially lifesaving technology" (9/1).