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INTRODUCTION

Tuberculosis (TB) is a severe and contagious disease caused by Mycobacterium 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 Starting in the 1940s, major medical advances brought effective treatment capable of curing the vast majority of clinical cases.3,4 TB continues to cause more than a million deaths worldwide every year. The morbidity and mortality burden of TB is unevenly distributed throughout the globe, disproportionately affecting those living in poverty and those from resource-limited settings.5

EPIDEMIOLOGY AND MICROBIOLOGY

In this section, aspects of the epidemiology and microbiology of TB are presented.

Global Burden of TB and Recent Progress

In 1990, the World Health Organization (WHO) declared TB a global emergency. In response, the WHO endorsed 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.8,9 By 2020, an estimated 60 million lives had been saved.10 Since 2004, TB incidence has been slowly falling every year, with an estimated reduction of 2.3% between 2018 and 2019.10 The Joint United Nations Programme on HIV/AIDS set the 90/90 goals, aiming to reach at least 90% of people with TB and ensure that at least 90% of them have a successful treatment completion.11 However, at the current pace, it is unlikely that these goals will be met by 2030 as originally proposed. Furthermore, these gains may be set back by disruption to TB control services during the COVID pandemic.10

Although global TB incidence is falling, TB remains one of the leading causes of global infectious mortality, and the 10th leading cause of death worldwide.10,12,13 In 2019, there were an estimated 10 million new TB cases, with 1.2 million deaths among HIV-negative people, and an additional 208,000 deaths among HIV-positive people. Moreover, many TB deaths occur in young, previously healthy adults, and as such, in 2019 TB was the 9th leading cause of lost disease-adjusted life years (DALYs).7,14

Poverty and TB

Globally, TB disproportionately impacts those with greater poverty and lower human development indices.15–18 Population health factors such as water sanitation, childhood immunization rates, and life expectancy also independently predict TB incidence.19,20 The vast majority of the global burden of TB is concentrated in low- and middle-income countries (LMICs), with 28 of the 30 highest-burden countries located in Africa and Asia10 (Fig. 130-1, Table 130-1).

Figure 130-1

Estimated TB incidence by ...

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