Newer and novel insights into the pathogenesis and treatment of drug-resistant tuberculosis

Methods: We analysed data on drug resistance among new and previously treated TB cases reported by countries to WHO up to 2012. Data are collected in surveys of a representative sample of TB patients or from surveillance systems in which diagnostic drug susceptibility testing is routine practice, and quality-assured by the Supranational TB Reference Laboratory Network. Findings: In 1994-2012, surveillance data on MDR-TB were reported from 136 countries worldwide. Global proportions of new and previously treated TB cases with MDR-TB were 3.6% (95% CI: 2.1-5.1) and 20.2% (95% CI: 13.3-27.2), respectively. The highest proportions are found in countries of the former Soviet Union (FSU), where in several countries more than 20% of new cases and more than 50% of previously treated cases have MDR-TB. Estimated MDR-TB incidence rates (MDR-TB cases per 100,000 population) are highest in FSU countries and in southern Africa. Extensively drug-resistant TB (XDR-TB) has been reported by 92 countries. On average, an estimated 9.6% (95% CI: 8.1%–11%) of MDR-TB cases have XDR-TB. A significant positive association between HIV and MDR-TB has been shown in 12 countries. Between 1994 and 2012, data on time trends in drug resistance were available from 88 countries and 10 territories worldwide for a total of 870 country-year data points. Rates of MDR-TB in the general population increased in Botswana, United Kingdom, and in Oblasts of the Russian Federation and declined in Latvia, Estonia, and the United States of America. Conclusion: Better data from continuous surveillance or surveys are required, especially from Africa and India. Trends in MDR-TB are still unclear in most settings. Surveys should be repeated more frequently using molecular technologies to monitor the MDR-TB epidemic more effectively.