2.6 Risk factors for developing active TB

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The risk depends on a number of factors including those that lead to a weakened immune system, damaged lungs, or the intensity and duration of exposure. Examples for each of these conditions are as below:

2.6.1 Weakened host immune defences

  • HIV infection
  • Diabetes mellitus
  • Malnutrition
  • Prolonged therapy with corticosteroids (such as prednisolone) and other immuno – suppressive therapies
  • Certain types of cancer (e.g., leukaemia, Hodgkin's lymphoma, or cancer of the head and neck)
  • Severe kidney disease
  • Alcoholism
  • Substance abuse
  • Age
    • Young children (children under 5 have twice the risk and higher risks are observed for those under 6 months)
  • Pregnancy

2.6.2 Conditions that damage the lung

  • Tobacco smoking
  • Silicosis

2.6.3 Intensity of exposure (number of inhaled bacilli)

  • Infectiousness of the source
  • Environment in which the exposure took place and proximity to the source.
  • Duration of exposure
  • Inhabitants of high-risk congregate settings (crowded and ill ventilated residence and / or workplace)