What is tuberculosis?

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Tuberculosis, or TB, is a chronic infectious disease caused by a bacterium called Mycobacterium tuberculosis. It usually affects the lungs, but can attack other parts of the body. It is mainly spread by breathing in air-borne bacteria from people with active infectious TB disease.

The bacteria can destroy parts of the lungs, making it difficult to breathe.

Bacteria can spread to, and damage other parts of the body, such as the digestive and urogenital tracts, bones, joints, nervous system, lymph nodes and skin. This is called extrapulmonary TB, and is far less common. The disease is characterised by the development of granulomas or tubercles in infected tissues.

While TB is a global problem and undeveloped countries usually have much higher incidences than developed countries. South Africa has one of the highest reported TB infection rates in the world. In some parts of the world, including South Africa, TB is the most important opportunistic infection of people with HIV.


Worldwide prevalence

  • According to the World Health Organisation, tuberculosis is second only to HIV/Aids as the greatest killer worldwide due to a single infectious agent.
  • People of all ages, nationalities and socioeconomic groups can get TB. In 2013, nine million people fell ill with TB, while 1.5 million died from the disease.
  • Over 95% of TB deaths occur in low- and middle-income countries. It is among the top three causes of death for women aged 15 to 44, with almost half a million women dying from TB in 2013 alone.
  • Every country is vulnerable to the consequences of poor TB treatment practices in others.
  • People with untreated TB disease could infect another 10 to 15 people each year.
  • TB is the leading infectious killer of people with HIV/Aids, accounting for almost one in four Aids deaths. HIV and TB each speed the other's progress.
  • 80% of TB sufferers are in their most economically productive years.
  • Five to 10% of people infected with TB become sick or infectious during their lifetime, compared to those with a decreased immunity e.g. due to HIV/Aids. They have a much higher risk of almost 10% every year.

Factors that contribute to the increase in global TB prevalence are:

  • Increasing number of HIV/Aids cases.
  • Drug-resistant TB strains. Evidence now indicates that drug resistant strains are transmitted within the community e.g. in schools, taxis, shebeens etc.
  • Population mobility. Global trade and air travel have increased greatly since 1960. Numbers of refugees and displaced people have increased nine-fold in 20 years.
  • TB spreads quickly in crowded refugee camps and shelters and it is difficult to treat mobile populations. Other displaced people such as homeless people in industrialised countries are at risk.
  • Closed communities (e.g. prisons and mines) have a higher incidence of TB and contribute to the increase in prevalence.

Prevalence in South Africa

  • TB has reached epidemic proportions in South Africa, with the WHO confirming that the country has one of the worst tuberculosis epidemics in the world.
  • South African TB disease rates are up to 60 times higher than those in the USA or Western Europe. In 2013, about 330 000 South Africans had TB disease, of which 90 000 died.
  • The incidence rate in South Africa is an estimated 860 cases per 100 000 population. Incidence rates differ among provinces; for example, the Western Cape has close to 1,000 per 100 000 population. Incidence rates in prisons and among minors are also much higher and can approach 2,500 per 100 000 population.
  • Close to 70% of all TB patients are also HIV-positive.
  • TB is the leading infectious killer of youths and adults. About two thirds of the population are infected with TB, although most will not get the disease. 

Read more: 

Symptoms of tuberculosis 

Diagnosing tuberculosis  

Preventing tuberculosis  

Reviewed by Dr AW Dreyer, Pathologist and Clinical Microbiologist, Centre for Tuberculosis, National Institute for Communicable Diseases February 2015.

Previously reviewed by Joanna Evans, PhD, Molecular Mycobacteriology Research Unit, Division of Medical Microbiology Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, February 2011.

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