Tuberculosis (TB) is a severe and contagious disease caused by infection with members of the Mycobacteria tuberculosis complex (MTBC). Most often involving the lungs, TB is transmitted by cough, with an infectious dose of less than 10 bacteria.1 Case fatality rates in untreated active pulmonary TB approach nearly 60%.2 Major medical advances of the past half-century have brought effective treatment capable of cure in nearly all identified cases.3,4 Despite this TB causes hundreds of thousands of deaths worldwide every year. The morbidity and mortality burden of TB is not uniformly distributed throughout the globe but rather disproportionately affects those living in poverty and those from resource-limited settings.5
Epidemiology and Microbiology
In this section, aspects of the epidemiology and microbiology of tuberculosis are presented.
Global burden of TB and Recent Progress
In 1990, the World Health Organization (WHO) declared TB a global emergency and in response, developed the directly observed therapy strategy (DOTS), promising to “Stop TB” by finding and treating infectious cases in resource-limited settings.6,7 Within a few years of its design, the World Bank labeled the DOTS strategy the most cost-effective health-intervention ever deployed and by 2012, an estimated 51 million people had been treated and an estimated 20 million lives saved.8–10 Since 2004, TB incidence is falling in all WHO regions and in each of the 22 highest burden countries.
Although global TB incidence is falling, TB remains a leading cause of global infectious mortality, second only to HIV infection.11,12 There were 8.7 million new cases of TB and 1.4 million deaths globally in 2011. Moreover, many TB deaths occur in young, previously healthy adults, and as such, TB is a top 10 cause of lost disease adjusted life years (DALYs).7
Broadly speaking, there are three major threats to global TB control: (1) Poor social conditions including inadequate housing and nutrition,5 (2) Immune compromise related to the HIV pandemic,2,13 and (3) Emergence of drug-resistant TB.14,15
Globally, TB distribution correlates closely with poverty and human development indices.16–19 Population health factors such as water sanitation, childhood immunization rates, and life expectancy also independently predict TB incidence.20,21 A corollary of these relationships is that only 1% of the global TB burden occurs in the industrially developed countries of North America and Europe while more than 90% arises in Asia and Africa (Fig. 131-1) (Table 131-1).10
Estimated TB incidence by Country 2011. (Reproduced with permission from 2012. Global Tuberculosis Report, World Health Organization.)
Table 131-1TB Incidence ...