Molecular Test Accurately Detects MDR-TB within Two Days

A molecular assay test, as opposed to conventional culture techniques, may revolutionize the diagnosis and reporting of multidrug-resistant tuberculosis (MDR-TB) in high-infection areas by delivering the critical results more quickly and perhaps even more accurately--thus enabling proper treatment to begin promptly.

MDR-TB is increasing and it spreads most rapidly through vulnerable communities that are already suffering from AIDS. One of the biggest barriers to appropriate treatment is the lengthy diagnostic process of conventional techniques that are not well suited to public health settings serving such populations.

"With continued delay of testing results, and thus, treatment, the patient will likely transmit the infection to those persons they come in close contact with,” said Richard O'Brien, M.D., senior investigator from the Foundation for Innovative New Diagnostics (FIND; Geneva, Switzerland), a nonprofit organization. "TB is already the leading cause of death among AIDS patients worldwide. This association is particularly lethal when drug-resistant TB is being transmitted. MDR-TB, with resistance to the most important anti-TB drugs, isoniazid and rifampicin, is even more lethal.”

A study, which appeared in the April 1, 2008, issue of the American Journal of Respiratory and Critical Care Medicine, was conducted by Dr. O'Brien and his colleagues in South Africa. They found that a molecular assay test, as opposed to conventional culture techniques, might revolutionize the diagnosis and reporting of MDR-TB in these high-infection areas.

The study took place in a national health laboratory in Cape Town, South Africa, which serves over 4.2 million people and processes about 400,000 specimens annually. The testing was performed on residual portions of specimens originally collected for other purposes. They were able to obtain interpretable results within one to two days in 97% of smear-positive samples, and had a better than 98% specificity and sensitivity rate for multidrug resistance.

"The advantage of this test, based on its performance in the lab in South Africa, is its equivalent or perhaps increased accuracy compared to standard methods and an increase in the number of interpretable results, as standard techniques are subject to contamination,” said Dr. O'Brien. "Additionally, it only takes one to two days, as opposed to the mean turnaround time of 42 days with conventional cultures.”

The two to three months that conventional techniques can take to determine drug resistance can be fatal to an HIV-infected patient. Complicating the picture is the danger of MDR-TB becoming XDR-TB--extensively drug resistant. "If patients receive inappropriate treatment because of the lack of proper screening, the risk of developing increasingly resistant and consequently, virtually untreatable strains of TB in these already vulnerable populations is much higher,” said Dr. O'Brien. "This test is now being evaluated in program conditions in a number of countries where MDR-TB is epidemic. We expect that more widespread use of this test will be a great improvement in our ability to address this serious problem that threatens the global control of tuberculosis.”

Such an improvement in diagnosis in public health settings could take clinicians treating TB in high-burden areas out of ‘the dark,'” said Max Salfinger, M.D. and David Ashkin, A.G., in an editorial in the same issue of the journal.


Related Links:
Foundation for Innovative New Diagnostics