KHOPOTSO: With any form of TB, normal or drug-resistant, there are problems with late diagnosis. By the time that patients are diagnosed, they might have infected a few other people. That’s how TB spreads. With drug-resistant TB, if health-care workers take time to suspect that an individual may be carrying it, then that’s another opportunity lost while the person may be transmitting it to others. But not only does the problem lie there. Techniques used in the laboratory to test for TB in specimens ‘ the raw spit that patients cough up – are not quick enough to confirm a TB result, says Dr Xoliswa Poswa a pathologist with the National Health Laboratory Service (NHLS), in Johannesburg.
Dr XOLISWA POSWA: The technology that we have right now’¦ depends on what we call ‘culture’. We grow the organism in the laboratory. It takes a minimum of about two weeks just to get that organism growing and to be able to inform the health-care worker that there is TB or, possibly, the resistant form. But before we even tell you that it’s resistant, it’s two weeks first for growing it and another two weeks to grow it in the presence of the drug that the clinician would like to use. So, it’s basically a minimum of four weeks before the clinician knows that they are using the correct treatment or not.
KHOPOTSO: Poswa says that, while the culture and drug testing method that is currently being used is specific enough to make a diagnosis, the process is far too long. As a result, scientists are devising alternative, quicker forms of diagnosis.
Dr XOLISWA POSWA: There are two tests that we’re going to be looking at here, the ones that are going to give us a rapid diagnosis. One is a molecular test. It looks at the genes: Do we have the DNA for TB here? And if we do have it, does it show genes that are consistent with resistance to the two drugs that we are specifically interested in? And then, the other test performs like our usual test’¦ But it’s quite an ingenious test that allows you to see within 48 hours that there is, possibly, growth of bacteria there.
KHOPOTSO: Patients with multi-drug resistant or MDR TB typically fail to respond to treatment using Isoniazid and Rifampicin, the main drugs in the treatment of tuberculosis. With Extremely Drug-Resistant or XDR TB, patients do not respond to the two drugs, including some of the additional drugs used in second-line treatment. If the proposed rapid test for TB proves successful, it could significantly cut short the gap between diagnosis and the initiation of appropriate treatment.
Dr XOLISWA POSWA: This test is going to give us an answer within a space of 24 ‘ 48 hours. It is a screening test, marked improvement from waiting a minimum of two weeks.
Even if you still need to grow it, most of the clinicians or most of the patients will have an indication and treatment would be started immediately ‘ and correct treatment, for that matter ‘ because if you are treating a patient that already has drug-resistant TB, treating it with the drugs for normal TB’¦ that is assisting transmission of drug-resistant TB. So, that’s going to make a big difference to the lives of patients.
KHOPOTSO: The Department of Health’s figures from two years ago, show that about 645 South Africans out of every 100 000 have TB. HIV, a twin epidemic of TB, is influencing the growth of tuberculosis infections. Professor Shabir Madhi is Co-Director of Wits University’s Respiratory and Meningeal Pathogens Research Unit (RMPRU), based at Chris Hani Baragwanath Hospital, in Soweto.
Prof. SHABIR MADHI: There’s been an exponential increase in the burden of adult TB, and what that basically means is that there’s much more infectious adults in South Africa than there were before the HIV epidemic. Now, the way children are affected by this, is that children are usually infected by TB because of the infectious adults in the community’¦ When a child becomes infected with TB, the risk of them actually developing disease from the infection is about 40% in the first two years of life. If a completely healthy adult becomes infected with TB, the lifetime risk of that adult actually developing disease from that infection is only about 10%.
KHOPOTSO: The proposed rapid test for TB could, hopefully, work to catch those infectious adults. According to Dr Poswa, a large-scale one-year long trial by the National Health Laboratory Service, the Department of Health and the Medical Research Council of South Africa is due to start in April.
Dr XOLISWA POSWA: They are looking at testing about 20 000 patients, nationally’¦ But from the little we’ve seen in the laboratory in comparing this new test with the culture, which is currently our gold standard, it looks promising. We have done some preliminary tests’¦ but we need to’¦ be sure of what we’re doing before we roll it out.