Rapid Tuberculosis Test Will Have Worldwide Impact

An innovative test platform that uses polymerase chain reaction (PCR) technology to diagnose tuberculosis (TB) in less than two hours represents new hope for millions of people around the world.

The Xpert Mycobacterium tuberculosis/resistance to rifampicin (MTB/RIF) test identifies TB in 98% of active cases--an improvement of more than 45% on one of the most commonly used current techniques. It also detects whether the TB-causing bacteria are resistant to rifampicin, a first-line drug for TB, in nearly 98% of cases. A single test can also diagnose TB in 72% of those infected with both HIV and TB, which the current standard smear test cannot do at all. A second and third round of testing brings the Xpert MTB/RIF's sensitivity up to 90%.

Xpert MTB/RIF relies on real-time PCR technology, which generates thousands to millions of copies of a section of the DNA of the TB bacterium. The process is mostly automated, reducing contamination of the sample, and does not need much equipment, giving it great potential for use in resource-poor clinics in the developing world where it can be carried out by technicians with minimal training. The test is based on a platform developed by the US government to detect the anthrax bacterium (Bacillus anthracis). The Xpert MTB/RIF test runs on the Cepheid (Sunnyvale, CA, USA) GeneXpert system.

"If you were to inoculate an Xpert MTB/RIF test at the same time you started preparing your acid fast smears, by the time you finished reading the smears, the Xpert MTB/RIF test result would be ready, telling you if your positive acid fast smear was TB and if the strain was resistant to rifampicin, which is an excellent surrogate marker for MDR-TB. I'm sure Koch and Pasteur would not only be delighted with the technological advance, they would probably say, ‘It's about time',” said Fred Tenover, PhD, senior director of scientific affairs at Cepheid.

According to the World Health Organization (WHO, Geneva, Switzerland), Mycobacterium tuberculosis is considered to be vastly under diagnosed. This is a direct result of current testing methods requiring weeks to deliver a definitive result, which can lead to patients being left untreated or placed on ineffective therapies. These patients may continue to spread the disease to others in the community, increasing the disease burden. And with the worldwide reemergence of TB, multidrug resistant (MDR) and extensively drug resistant (XDR) strains have become an even greater threat; current testing for drug resistance can take more than 4 weeks, leading to higher mortality and the further spread of MDR strains.

Related Links:
Cepheid
World Health Organization