This article waslast modified on 10 July 2017.
The diagnosis of active pulmonary tuberculosis (TB) is likely if the sputum of a patient with suggestive symptoms is found to contain bacilli that stain in a specific way when examined under the microscope. However, to make a definitive diagnosis and to find out the best drugs for treatment, the bacilli have to be grown in culture. This can take from a few days to six to eight weeks. More rapid diagnostic tests that examine the molecular structure of the organism’s DNA give results within about eight hours. However, because they must be carried out in specialised laboratories by highly skilled staff, these tests are available to only a very small proportion of the more than nine million people worldwide that the World Health Organization estimates become infected with TB each year. Delay in diagnosis and treatment leads to increased spread of the disease and increased mortality.

A new rapid automated molecular test system (Xpert MTB/RIF) can detect TB and find out whether it is resistant to the drug rifampicin in less than two hours. The system needs minimal hands-on time and can be operated by relatively unskilled workers without laboratory facilities. Its development was supported by the Foundation for Innovative New Diagnostics (FIND), Geneva and the University of Medicine and Dentistry of New Jersey in collaboration with a commercial partner, Cepheid.

The test system results on sputum specimens from 1462 people from Peru, Azerbaijan, South Africa and India with symptoms suggestive of active TB of the respiratory tract were reported in the New England Journal of Medicine on 9 September 2010. The investigation was funded by FIND, the National Institutes of Health, Cepheid and the Bill and Melinda Gates Foundation. The test results were compared with the microscope examination of sputum smears and with sputum cultures as the “gold standard”. The new test correctly identified 98.2% of 561 smear and culture positive subjects and 99.2% of 609 who were smear and culture negative. Of those smear negative but culture positive, three repeated tests identified 90.2%. The test correctly identified 97.6% of rifampicin-resistant and 98.1% of rifampicin-sensitive TB.

The researchers believe that the simplicity and safety of the system could allow for cost-effective and highly sensitive detection of TB and drug resistance outside reference centres. Increased access would decrease delays in diagnosis without the need to build large numbers of laboratories equipped for advanced protection of lab staff from infection.