The "Source" of Drug-Resistant TB Outbreaks

Abstract

Much has recently been written about extensively drug-resistant tuberculosis (XDR TB) outbreaks in South Africa (“Extensively drug-resistant TB gets foothold in South Africa,” J. Cohen, News of the Week, 15 Sept., p. [1554][1]). Although mono-, multi-, or extreme drug resistance can be acquired in a strain of Mycobacterium tuberculosis through inappropriate therapy or poor compliance, this is arguably infrequent. In South Africa, XDR TB has been reported as an “outbreak,” which implies transmission by definition. The real problem from a public health perspective, therefore, is to prevent transmission. Transmission can occur almost anywhere, and this problem is exacerbated in immune-compromised individuals. In much of the developing world, treatment relies on smear-based diagnosis followed by a standard regimen of first-line drugs and monitoring for sputum conversion at 2 to 3 months. In the absence of conversion, the patients are classified as possible resistance cases, and samples are sent for limited resistance testing (usually to the drugs isoniazid and rifampin only). Only if resistance to these is confirmed are further tests requested. Even then, testing is not routinely done for all antibiotics, so there can be a continuation of treatment with inappropriate antibiotics, ongoing transmission, and further acquisition of resistance. A proactive intervention is needed where the full spectrum of tests for all antibiotics are used at the outset. This is not generally part of most programs, partly because of the cost and difficulties involved. With the help of the local health authority and implementation of rapid molecular tests, we were able to stop a multidrug-resistant TB outbreak in the Cape Town environment by PCR-based genotyping of isolates and rapid intervention. Unless we accelerate diagnosis, we will not defeat TB. [1]: /lookup/doi/10.1126/science.313.5793.1554a