Introduction

Tuberculosis (TB) is an infectious disease that can affect any organ in the body, although the vast majority of cases involve only the lungs. Transmission of the disease occurs from person to person via the airborne route. When an untreated individual with active TB coughs, droplet nuclei containing the TB bacillus are expelled into the air and can be inhaled by others in close proximity. Beginning in the late 1940s antibiotics were developed that were effective in curing TB. However, mutant strains of TB that were resistant to one or more of these antibiotics began to be identified as early as 1956. Since then, the evolution of antibiotic resistance among TB has been a growing problem that is now a major public health threat. Multiple drug resistant TB (MDR-TB) refers to strains of TB that are resistant to at least isoniazid and rifampin, two of the first-line antibiotics used in treatment. As the problem continued to grow, the term XDR-TB was coined for extensively drug resistant TB. XDR-TB is resistant to at least four of the first line anti-TB drugs, i.e., resistance to not only isoniazid and rifampicin, but also resistance to any of the fluoroquinolones and to at least one of three injectable second-line drugs (amikacin, capreomycin or kanamycin). MDR-TB and XDR-TB both take substantially longer to treat than ordinary (drug-susceptible) TB and require the use of second-line anti-TB drugs, which are more expensive and have more side-effects than the first-line drugs used for drug-susceptible TB. This module will focus on MDR-TB and XDR-TB.

Key Facts About TB from the World Health Organization (WHO)
Tuberculosis (TB) is second only to HIV/AIDS as the greatest killer worldwide due to a single infectious agent. In 2012, 8.6 million people fell ill with TB and 1.3 million died from TB. Over 95% of TB deaths occur in low- and middle-income countries, and it is among the top three causes of death for women aged 15 to 44. In 2012, an estimated 530 000 children became ill with TB and 74 000 HIV-negative children died of TB. TB is a leading killer of people living with HIV causing one quarter of all deaths. Multi-drug resistant TB (MDR-TB) is present in virtually all countries surveyed. The estimated number of people falling ill with tuberculosis each year is declining, although very slowly, which means that the world is on track to achieve the Millennium Development Goal to reverse the spread of TB by 2015. The TB death rate dropped 45% between 1990 and 2012. An estimated 22 million lives saved through use of DOTS and the Stop TB Strategy recommended by WHO About 450 000 people developed MDR-TB in the world in 2012. More than half of these cases were in India, China and the Russian Federation. It is estimated that about 9.6% of MDR-TB cases had XDR-TB.

Key Facts About TB from the World Health Organization (WHO)

Tuberculosis (TB) is second only to HIV/AIDS as the greatest killer worldwide due to a single infectious agent.
In 2012, 8.6 million people fell ill with TB and 1.3 million died from TB.
Over 95% of TB deaths occur in low- and middle-income countries, and it is among the top three causes of death for women aged 15 to 44.
In 2012, an estimated 530 000 children became ill with TB and 74 000 HIV-negative children died of TB.
TB is a leading killer of people living with HIV causing one quarter of all deaths.
Multi-drug resistant TB (MDR-TB) is present in virtually all countries surveyed.
The estimated number of people falling ill with tuberculosis each year is declining, although very slowly, which means that the world is on track to achieve the Millennium Development Goal to reverse the spread of TB by 2015.
The TB death rate dropped 45% between 1990 and 2012.
An estimated 22 million lives saved through use of DOTS and the Stop TB Strategy recommended by WHO

About 450 000 people developed MDR-TB in the world in 2012. More than half of these cases were in India, China and the Russian Federation. It is estimated that about 9.6% of MDR-TB cases had XDR-TB.

Additional information on TB and how it spreads can be found at http://www.cdc.gov/tb/.

Learning Objectives

Define and distinguish MDR-TB and XDR-TB.
Explain the mechanisms by which resistance occurs.
Describe the means of transmission.
Describe the role of direct observation therapy (DOT) and its importance in preventing the spread of MDR-TB.
Discuss potential consequences of not controlling the spread of MDR-TB and XDR-TB.
Summarize the ongoing initiatives to control MDR-TB and XDR-TB on a global stage.

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