Tuberculosis Causes

By Dr Ananya Mandal, MD

Tuberculosis is an infectious disease and is caused by a type of bacterium called Mycobacterium tuberculosis. One-third of the world's population is infected with the bacterium that causes tuberculosis. Each year about nine million people develop the disease and up to nearly two million people worldwide are killed by it.

How is TB spread?

The infection is spread when a person with an active TB infection in their lungs coughs or sneezes near a person without the infection. The bacterium is released in the expelled droplets and is inhaled by the healthy person.

Tuberculosis, however, is not a contagious disease unlike other infections like flu, the common cold etc. It affects people with a lowered immunity more commonly than those with an intact immune system.

Risk factors for TB

Risk factors associated with getting tuberculosis include:-

  • People living in areas with a high prevalence of tuberculosis.
  • People who work closely or live close to a person with infectious tuberculosis. This includes healthcare workers and people living in crowded living spaces. Children in schools and prisoners living in closed confined spaces are at a greater risk.
  • Travellers to areas with high incidence of tuberculosis and immigrants from countries with high incidence are at risk of bringing the infection to countries where the prevalence of the condition is lower.
  • Those with other infections like HIV have a lower capacity to fight off tuberculosis. This is mainly due to depressed immune system caused by the concomitant HIV infection. Those with medical conditions such as diabetes, immune disorders, end-stage renal disease, gastrectomy/jejuno-ileal bypass, those taking drugs like corticosteroids for long durations, those on chemotherapy for cancer and other drugs that suppress immunity (e.g. drugs used after organ transplants) are at a greater risk of tuberculosis.
  • Immature immunity for example in babies and declining immunity in the elderly makes both these age groups susceptible to tuberculosis. Pregnant women are also at a greater risk due to lowered immunity.
  • Malnutrition with a poor health or having a poor diet due to lifestyle, drug abusers, alcoholics, those living in poverty, the homeless etc. are more at risk of tuberculosis.

Reviewed by , BA Hons (Cantab)

Further Reading

Last Updated: Jan 29, 2013

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