Belinda Beresford, Mail & Guardian
The test used in the study is not only much faster than existing methods, it is at least as accurate and potentially much cheaper. The South African researchers worked with an international NGO, the Foundation for Innovative New Diagnostics (Find) and used a conventional molecular assay, GenoType MTBDRplus. Molecular assays look for mutations known to confer drug resistance in the genetic material of the TB bacillus, rather than relying on responses of bacterial colonies to different antibiotics.
Standard laboratory procedures can take weeks to detect drug resistance because they have to grow the TB bacteria, Mycobacterium tuberculosis, from samples and the bacterium reproduces very slowly. Rapid diagnosis of drug resistance is crucial for the successful treatment and the prevention of the further spread of such forms of the disease. Treatment of drug-susceptible TB takes about six months and is relatively cheap and effective. Drug resistant TB can take two years to treat and the success rate is much lower. Tuberculosis is the single main killer of HIV-positive individuals, with the two diseases reinforcing each others destructive impact at a cellular level. Most of the HIV-positive patients known to have extensively drug resistant TB have died shortly after diagnosis. The study in Cape Town, which was reported in the American Journal of Respiratory and Critical Care Medicine, was the first to show that molecular assays can be successful in a routine, high volume, high-TB setting.
The Greenpoint NHLS site handles more than 1 000 sputum samples a day and services a population of about 4,25-million people. In the laboratorys catchment area there are 932 new cases of TB per 100 000 people diagnosed each year. Of the 536 samples tested almost one in five contained drug resistant tuberculosis. The Medical Research Council, the NHLS and Find are now working with the different provincial departments of health to look at the feasibility, impact and cost effectiveness of using these tests in South Africa. The results produced by the Greenpoint laboratory have since been replicated by other NHLS laboratories around the country. Heidi Albert of Find, who participated in the study, says that in the next year more than 20 000 patients in four provinces who are at risk of multidrug-resistant TB -- usually because of failed previous TB treatment -- will be tested with these molecular assays. The results will be used to improve drug-resistance detection in South Africa and other countries with high levels of TB. According to the latest statistics from the World Health Organisation South Africa has the seventh-highest burden of TB in the world.