Cape Town lab nails TB rapid diagnostic test.

A molecular assay test, as opposed to conventional culture techniques, may revolutionise the diagnosis and reporting of 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.

The study took place in a national health laboratory in Cape Town 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 1-2 days in 97% of smear-positive samples, and had a better than 98% specificity and sensitivity rate for multidrug resistance. One of the biggest barriers to appropriate treatment is the lengthy diagnostic process of conventional techniques poorly suited to public health settings serving vulnerable 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 Dr Richard O'Brien, senior investigator from the Foundation for Innovative New Diagnostics, a non-profit organisation funded in part by USAID and the Bill & Melinda Gates Foundation, which sponsored the study. '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.'

The study is reported in the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society. 'The advantages of this test, based on its performance in the lab in South Africa, are 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 1-2 days, as opposed to the mean turnaround time of 42 days with conventional cultures.'