Multidrug resistant tuberculosis is now thought to afflict between 1 and 2 million patients annually. Although significant regional variability in the distribution of disease has been recorded, surveillance data are limited by several factors. The true burden of disease is likely underestimated. Nevertheless, the estimated burden is substantial enough to warrant concerted action. A range of approaches is possible, but all appropriate interventions require scale-up of laboratories and early treatment with regimens containing a sufficient number of second-line drugs. Ambulatory treatment for most patients, and improved infection control, can facilitate scale-up with decreased risk of nosocomial transmission. Several obstacles have been considered to preclude worldwide scale-up of treatment, mostly attributable to inadequate human, drug, and financial resources. Further delays in scale-up, however, risk continued generation and transmission of resistant tuberculosis, as well as associated morbidity and mortality.
KeywordsTuberculosis; drug resistance; surveillance; management; epidemiology An estimated 489,139, or nearly 5% of all new cases of tuberculosis (TB) diagnosed in 2006 were multidrug resistant (MDR), that is resistant to isoniazid and rifampicin, the two most effective anti-TB agents. This represents an increase of 12% since 2004 and 56% since 2000. 1 An additional 1 to 1.5 million prevalent cases of MDR-TB were estimated in 2006, resulting in as many as 2 million people with active disease. 2 The successful treatment of MDR-TB requires the use of second-line drugs, which historically presented an insurmountable cost barrier in resource-poor settings. To alleviate this gap, the World Health Organization (WHO) established the Green Light Committee (GLC) in 2000 to facilitate access to and strictly supervise the use of second-line agents for TB control.Even with the inception of the GLC and a significant reduction in cost of second-line drugs, drug resistant TB continues to grow and challenge the current capacity in most settings. Recognition of the magnitude of the MDR-TB problem and its associated morbidity and mortality has motivated recent calls for increased research and scaled-up treatment. 3,4 Several recent, excellent articles have reviewed the molecular mechanisms of resistance, risk factors for drug resistant TB (DR-TB), DR-TB and HIV, and global epidemiology of TB. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] This article highlights the gaps in knowledge of the global epidemiology of MDR-TB, illustrates
EPIDEMIOLOGY OF MDR-TB Drug Resistance and Multidrug TherapyDR-TB is defined as tuberculosis caused by a strain of Mycobacterium tuberculosis that grows, in vitro, in the presence of one or more antimycobacterial drugs. Spontaneous mutations leading to resistance occur at random in large populations of M. tuberculosis at a rate per cell division of 10 −10 for rifampin (RIF), 10 −8 for isoniazid (INH) and streptomycin, 10 −6 to 10 −8 for fluoroquinolones, 10 −7 for etham...