Anti-Tuberculosis Drug Resistance in the World. Report No. 2 Prevalence and Trends
The WHO/IUATLD Global Project on Anti-Tuberculosis Drug Resistance Surveillance WH0/CDS/TB/2000.278
Document produced by the WHO Global Tuberculosis Programme
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English     2000        253   pages
Table of contents
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This report presents the latest findings of a major collaborative study aimed at measuring the prevalence of anti-tuberculosis drug resistance throughout the world. Drawing on data collected from 1997-2000, the report covers the second phase of a global project organized by WHO, the International Union Against Tuberculosis and Lung Disease (IUATLD), and other partners. The project was launched in 1994 in response to growing concern about the problem of drug-resistance and its potentially dramatic impact on the epidemiology and control of TB.
Apart from documenting the true magnitude of the problem, the project aims to ensure that policy recommendations for national TB control are backed by accurate and representative data. Particular attention is given to the role of WHO recommendations, which advocate the use of short-course chemotherapy and directly-observed treatment, in preventing the emergence of resistant strains of Mycobacterium tuberculosis or containing their spread. The project's first report was issued in 1997.
This second report represents both a considerable expansion in the number of geographical settings covered and a continuing refinement of the rigorous methodology used to collect data, verify their quality, and ensure correct interpretation. The report also marks the first opportunity to evaluate global trends in drug resistance over time. As of December 1999, 72 geographical settings had been surveyed to assess the magnitude of drug resistance and monitor trends.
Trends in resistance to any drug are covered together with trends in the prevalence of multidrug-resistant tuberculosis (MDR-TB), which is defined as resistance to at least isoniazid and rifampicin. The report also marks the first attempt to measure the impact of migration on the distribution of drug-resistant TB within a given country.
The report has four chapters. The first introduces the global project, and considers some of the factors associated with the emergence of drug-resistant M. tuberculosis in a population. Chapter two, on methods, explains how the vital need for accurate susceptibility testing is being met through the project's rigorous methodology, which relies on an international system of proficiency testing backed by a unique network of supranational reference laboratories.
Key findings are presented in the third chapter, which draws on data collected from 58 geographical settings. Results are presented separately for drug resistance among new cases, drug resistance among previously treated cases, and combined drug resistance. For the first time, trends over time are also presented and discussed.
While the study found drug-resistant TB in all settings, the magnitude of the problem varied widely across regions. MDR-TB among new cases was found to be most severe in Estonia, Latvia, the oblasts of Ivanovo and Tomsk in Russia, Henan Province in China, and Iran. Other areas of concern include Zhejiang Province in China, Tamil Nadu State in India, and Mozambique.
While data indicate that importation of drug-resistant M. tuberculosis into low-incidence countries is a substantial problem, most of the imported strains are not multidrug-resistant. Data further suggest that HIV infection is not an independent risk factor for either drug resistance or MDR-TB.
The final and most extensive chapter discusses findings in terms of their policy implications for national TB control. A critical review of the magnitude of drug-resistant TB on each continent includes abundant advice on the significance of trends and the corresponding priorities for control at both national and global levels. The chapter also considers how migration from countries with different levels of drug resistance can affect control programmes, and explores the complex factors that contribute to the emergence or spread of drug resistance.
Recommendations underscore the importance of good TB control programmes as the most reliable way to contain and decrease resistance. On the positive side, data collected during the study show that MDR-TB has not increased to a significant degree in geographical settings implementing sound TB control. Moreover, several settings with good control programmes have seen significant decreases in the prevalence of any drug resistance among previously treated cases.