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Global tuberculosis: perspectives, prospects, and priorities.

Despite being nearly 100% curable, tuberculosis remains a major public health problem, representing the second leading cause of death from infectious diseases globally, with drug-resistant tuberculosis increasingly common. In 2012, an estimated 8.6 million people developed tuberculosis worldwide—a global incidence rate of 122 persons per 100 000 population—and 1.3 million people died. Incidence rates vary from high in southern Africa (550/100 000 population in Mozambique and Zimbabwe and 1000/100 000 population in South Africa) to fewer than 10/100 000 population in the United States, Canada, and most of Western Europe.1 Although the global prevalence of multidrug-resistant tuberculosis was estimated at 3.6% of newly diagnosed and 20.2% of previously treated patients, these rates were 20% to 35% for newly diagnosed cases and 50% to 69% for retreatment cases in the Russian Federation and some other former Soviet republics. In sub-Saharan Africa, the tuberculosis epidemic is driven by HIV through both increased reactivation of latent tuberculosis infection and the increased risk of rapid development of disease soon after exposure to Mycobacterium tuberculosis because of HIV-induced immunodeficiency. There is lower tuberculosis incidence in Asia, but because Asia’s population is so much larger than Africa’s—more than 4 billion compared with about a billion—75% of the 5 million tuberculosis cases in the 22 highest-burden countries are in Asia. In these countries, crowding, poverty, and inadequate tuberculosis treatment completion rates contribute to the epidemic.2 Despite these statistics, marked progress has occurred since the World Health Organization (WHO) declared tuberculosis a global emergency 20 years ago. In 1995, fewer than 2 million patients were successfully treated using the WHO’s Directly Observed Treatment, short course (DOTS) strategy, less than a quarter of the estimated total; by 2011, nearly 5 million patients were treated successfully with DOTS. Approximately 56 million patients have been treated successfully since 1995, preventing an estimated 22 million deaths. However, every year about 3 million people with tuberculosis are missed by health systems. Mortality rates are declining, albeit slowly, in all regions of the world. Since 1990, the death rate associated with tuberculosis has decreased 45%, from 25 persons to 14/100 000 population, although rates vary widely between countries. The greatest risk to tuberculosis control is lack of implementation of effective and currently available strategies and tools. Tuberculosis control rests on 3 fundamental principles: prompt and accurate diagnosis, effective treatment begun immediately upon diagnosis and monitored until completion, and interruption of transmission. Diagnosis Microbiological examination of sputum smears for acidfast bacilli, despite limitations, remains the mainstay of diagnosis. Newer diagnostics provide greater sensitivity, particularly among children and persons with HIV infection (whose sputum smears are often negative), and can also identify rifampin resistance. These newer tests can enhance, but not yet replace, smear microscopy because of expense and requirements for suitable infrastructure, including stable electricity supplies. Early and accurate identification of tuberculosis can result in earlier treatment and decrease transmission, but only if treatment is promptly initiated.3