Thursday, April 12, 2007

The Emergence of XDR Tuberculosis: Implications for Public Health in Resource-limited Settings.

Extensively drug-resistant (XDR) tuberculosis is an emerging threat that has assumed public health dimension.
XDR tuberculosis, classified as cases that are resistant to three or more of the six second-line drugs for the disease, has a mortality rate of more than 85%. This is not altogether a new occurrence as XDR tuberculosis was first described more than a decade ago.
XDR tuberculosis is not the same as multi-drug resistant (MDR) tuberculosis. In the latter, Mycobacterium tuberculosis has become resistant to isoniazid and rifampicin.
South Africa is at the moment trying to contain an outbreak of XDR tuberculosis which has spread to all the country’s provinces. The WHO is sending a permanent staff to that country to help with the containment effort. The resistant strain of the Mycobacterium tuberculosis is said to have originated from the KwaZulu-Natal province. Experts are of the view that XDR tuberculosis has spread beyond South Africa citing the lack of adequate diagnostic capacity and poor notification mechanisms as the reasons why the outbreak is being under-reported by other countries. Mario Raviglione, director of Stop TB at WHO refers to the outbreak as an absolute emergency lamenting that the world is not responding quickly enough. A US$95 million dollar appeal made in Paris last October to combat this emerging threat has met little response.
We all know that the very existence of XDR tuberculosis is an indictment on our health systems since it reflects weaknesses in tuberculosis management which otherwise should minimize the emergence of resistance. Early, accurate diagnosis and timely institution of the appropriate curative regimen which are monitored for adherence are important steps in tuberculosis control. When drug regimens and tuberculosis control are sub-optimal, drug-resistant strains are selected which eventually proliferate and with repeated treatment errors, multi- and extensively-drug resistant strains are born.
Chances are that in most resource-poor settings, the scenario I painted above about tuberculosis management and inefficient health systems is often the rule rather than the exception. It follows then that if the status quo remains, tuberculosis might go beyond what we now know as XDR tuberculosis.
There is no easy panacea to this threat. But the panacea does exist; we must be ready to pay the price. Who wants to experience the torment of tuberculosis becoming an incurable disease?
Resource-poor settings need an effective disease control infrastructure beginning with strengthened rapid diagnostic capacity which is accessible and can be deployed at the point of care. This should be supported with unlimited access to quality first- and second-line drugs with mechanisms put in place to ensure adherence. Preventing spread is a challenge but it is doable. Special attention needs to be paid to the immune-suppressed patients because of their vulnerability. All HIV patients should be screened regularly for latent tuberculosis and antiretroviral drugs should not be delayed unnecessarily. As a matter of urgency, resource-poor settings must have access to drug-susceptibility testing which at the moment is mainly found in developed societies. The place of increased surveillance and research bordering on TB control cannot be overemphasized. And I suggest we hurriedly form enduring partnerships designed to urgently enhance the production of third line drugs which the world is taking lightly now.

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