Published in the journal PLOS One, the study analysed about 4,670 samples from TB patients from the Western and Eastern Capes as well as KwaZulu-Natal. Researchers from the universities of Stellenbosh and KwaZulu-Natal as well as Johannesburg’s Aurum Institute, then looked at drug resistance patterns of MDR-TB strains that were responsible for the majority of XDR-TB cases.
XDR-TB develops when MDR-TB strains – that are already resistant to so-called first-line treatment for regular TB – develop further resistant to second-line drugs used to treat MDR-TB.
The most widespread MDR-TB strain showed particularly high resistance to two first-line drugs, ethambutol and pyrazinamide, and the second-line drug ethionamide. According to authors, the study published in late 2013 suggests that the current MDR-TB drug regimen is ineffective in killing and preventing transmission of these highly drug-resistant strains.
“These regimens were ineffective as they did not take into account that a significant proportion of MDR-TB strains are resistant to two or three of the drugs included in the five-drug standardised MDR-TB treatment regimen,” says Rob Warren, professor in molecular biology and human genetics at Stellenbosch University’s Faculty of Medicine and Health Sciences.
MDR-TB is resistant to the most effective anti-TB drugs, while XDR-TB shows additional resistance to alternative drugs leaving few effective treatment options and resulting in very poor patient outcomes.
According to authors, the study debunks the common belief that South Africa’s growing XDR-TB problem has been spurred by MDR-patients defaulting on their treatment, and shifts the blame to the standard treatment regimen being ineffective and potentially promoting the amplification of resistance.
“This study, for the first time, clearly reveals the flaws of drug regimens in use in South Africa and suggests that poor treatment rather than patient non-adherence represents the major driver of the emergence of XDR-TB,” reads a statement by one of the lead researchers, Dr Borna Muller, an epidemiologist.
“These strains have been ‘bred’ inadvertently over the last decades through the use of only limitedly effective standardised treatment regimens and the absence of regular drug resistance testing,” adds Muller.
According to him, these strains are readily transmitted, quickly acquire additional resistance and may eventually become untreatable and also spread in the community.
Based on these findings, the researchers call for an immediate strengthening of the standard treatment for MDR-TB in South Africa. – Health-e News Service.