Tuberculosis is a bacterial disease caused by the pathogen, Mycobacterium tuberculosis (Mtb), which is transmitted between humans through the respiratory route and most commonly affects the lungs. Only about 10 percent of individuals infected with Mtb progress to active TB disease within their lifetime; the remainder of persons infected successfully contain their infection. One of the challenges of TB is that the pathogen persists in many infected individuals in a latent state for many years and can be reactivated to cause disease. The risk of progression to TB disease after infection is highest soon after the initial infection and increases dramatically for persons co-infected with HIV/AIDS or other immune-compromising conditions.
Until recently, the diagnosis of TB in most countries in the world was made by microscopic examination of stained smears of sputum of suspected patients; however, smear microscopy is capable of detecting only 50–60 percent of all cases. More sensitive methods of diagnosing TB and detecting resistance to drugs have recently become available and are being widely implemented. The time between the onset of disease and when diagnosis is made and treatment is initiated is often protracted, and such delays allow the transmission of disease.
The basic strategy to combat TB has been to provide diagnosis and treatment to patients with active disease, both to prevent death from the disease and to interrupt ongoing transmission from infectious individuals. Treatment of TB disease requires multiple drugs for many months. These long drug regimens are challenging for both patients and health care systems, especially in low- and middle-income countries (LMICs), where the disease burden often far outstrips local resources. Some regions have seen a rise in the incidence of drug-resistant TB which requires even longer treatment regimens with drugs that are more expensive and difficult to tolerate.In addition to early diagnosis of people with TB disease, other interventions include BCG vaccination and provision of preventive therapy to exposed contacts and HIV-infected people.
Despite progress over the past decade in TB control, major gaps persist. Many patients are undiagnosed and untreated, and case detection and treatment success rates remain too low in the high-burden countries. Ominously, rates of multidrug-resistant (MDR) TB—defined as resistance to the two major TB drugs, isoniazid and rifampicin—are rising globally (WHO 2011a) with the emergence of extensively drug-resistant (XDR) TB, resistant to many second-line drugs, as well as strains resistant to all current drugs.