Causes of Pulmonary Tuberculosis

Pulmonary tuberculosis (TB) is caused by the bacteria Mycobacterium tuberculosis (M. tuberculosis). You can get TB by breathing in air droplets from a cough or sneeze of an infected person. This is called primary TB.

In the United States, most people will recover from primary TB infection without further evidence of the disease. The infection may stay asleep or nonactive (dormant) for years. However, in some people it can reactivate.

Most people who develop symptoms of a TB infection first became infected in the past. However, in some cases, the disease may become active within weeks after the primary infection.

The following people are at higher risk for active TB:

• Elderly
• Infants
• People with weakened immune systems, for example due to AIDS, chemotherapy, or antirejection medicines given after an organ transplant

Your risk of contracting TB increases if you:

• Are in frequent contact with people who have the disease
• Have poor nutrition
• Live in crowded or unsanitary living conditions

The following factors may increase the rate of TB infection in a population:

• Increase in HIV infections
• Increase in number of homeless people (poor environment and nutrition)
• The appearance of drug-resistant strains of TB

In the United States, there are approximately 10 cases of TB per 100,000 people. However, rates vary dramatically by area of residence and socioeconomic class.