Causes

TB is caused by the bacterium Mycobacterium tuberculosis . When a person with active TB of the lungs coughs or sneezes, people nearby may inhale the bacteria. TB is easily spread in crowded conditions. It is also easily spread among people who are ill or have weakened immune systems.

Pathway to the Lungs

Mycobacterium tuberculosis is inhaled through the mouth and nose and travels down into the lungs causing TB.

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Risk Factors

These factors increase your chance of developing TB:

• Weakened immune system or chronic diseases (highest risk)
• HIV infection
• Malnutrition
• Intravenous drug use
• Alcoholism
• Leukemia , lymphoma , and other cancers
• Poorly controlled diabetes mellitus
• Severe kidney disease
• Corticosteroids
• Some medications used for treating rheumatoid arthritis and other diseases including etanercept , infliximab , and adalimumab
• Suppressed immune system caused by medications, such as drugs to prevent rejection of a transplanted organ
• Other risks factors include:
  • Silicosis (an occupational lung disease)
  • Living in crowded, indoor conditions (eg, homeless shelters, dormitories, military barracks)
  • Age (infants, young children, and elderly people)