General

Tuberculosis

• Infection and transmission
• Global and regional incidence
• HIV and TB
• Drug-resistant TB

Infection and transmission

Tuberculosis (TB) is a contagious disease. Like the common cold, it spreads through the air. Only people who are sick with TB in their lungs are infectious. When infectious people cough, sneeze, talk or spit, they propel TB germs, known as bacilli, into the air. A person needs only to inhale a small number of these to be infected.

Left untreated, each person with active TB disease will infect on average between 10 and 15 people every year. However, people infected with TB bacilli will not necessarily become sick with the disease. The immune system "walls off" the TB bacilli which, protected by a thick waxy coat, can lie dormant for years. When someone's immune system is weakened, the chances of becoming sick are greater.

• Someone in the world is newly infected with TB bacilli every second.
• Overall, one-third of the world's population is currently infected with the TB bacillus.
• 5-10% of people who are infected with TB bacilli (but who are not infected with HIV) become sick or infectious at some time during their life. People with HIV and TB infection are much more likely to develop TB.

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Global and regional incidence

The World Health Organization (WHO) estimates that the largest number of new TB cases in 2009 occurred in WHO's South-East Asia & Western Pacific regions, which accounted for 55% of incident cases globally. The African region accounts for 31% and among the 15 countries with the highest estimated TB incidence, 13 are in Africa, because of high rates of HIV coinfection.

It is estimated that 1.3 million deaths resulted from TB in 2007. There were an additional 456,000 deaths among incident TB cases who were HIV positive (these deaths are classified as HIV deaths in the International Statistical Classification of Diseases). Both the highest number of deaths and the highest mortality per capita are in the WHO Africa region, where HIV has led to rapid growth of the TB epidemic, and increases the likelihood of dying from TB.

In 2009, estimated per capita TB incidence was falling in five out of six WHO regions, but increasing globally due to population growth. The exception is the Europe region, where TB incidence is stable. Prevalence and mortality rates are falling globally in all the six WHO regions, The Americas, Eastern Mediterranean and South-East Asia are on track to achieve the halving of prevalence and death rates by 2015. The Western Pacific region is expected to meet the prevalence rate by 2015 but narrowly miss the mortality rate. The prevalence/mortality rates in Europe and African regions will likely not be met by 2015.

Click here to see the Estimated incidence

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HIV and TB

HIV and TB form a lethal combination, each speeding the other's progress. HIV weakens the immune system. Someone who is HIV-positive and infected with TB bacilli is many times more likely to become sick with TB than someone infected with TB bacilli who is HIV-negative. TB is a leading cause of death among people who are HIV-positive. It accounts for about 13% of AIDS deaths worldwide. In Africa, HIV is the single most important factor determining the increased incidence of TB in the past 10 years.

WHO and its international partners have formed the TB/HIV Working Group, which develops global policy on the control of HIV-related TB and advises on how those fighting against TB and HIV can work together to tackle this lethal combination. The interim policy on collaborative TB/HIV activities describes steps to create mechanisms of collaboration between TB and HIV/AIDS programmes, to reduce the burden of TB among people with HIV and the burden of HIV among TB patients.

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