TB bacteria become active if the immune system can’t stop them from growing. The active bacteria begin to multiply in the body and cause active TB disease. The bacteria attack the body and destroy tissue. If this occurs in the lungs, the bacteria can actually create a hole in the lung.

Some people develop active TB disease soon after becoming infected, before their immune system can fight the TB bacteria. Other people may get sick later, when their immune system becomes weak for another reason.

Babies and young children often have weak immune systems. People infected with HIV have very weak immune systems. Other people can have weak immune systems, too, especially people with any of these conditions:

  • Substance abuse
  • Diabetes mellitus
  • Silicosis
  • Cancer of the head or neck
  • Leukemia or Hodgkin’s disease
  • Severe kidney disease
  • Low body weight
  • Certain medical treatments (such as corticosteroid treatment or organ transplants)
  • Specialized treatment for rheumatoid arthritis or Crohn’s disease.