Infection can develop after inhaling droplets sprayed into the air from a cough or sneeze by someone infected with the Mycobacterium tuberculosis bacteria. Granulomas (granular tumors) develop in the infected tissue. The usual site of the disease is the lungs, but other organs can be involved. In the U.S., most people with primary tuberculous lesions will heal and will have no further evidence of disease. Disseminated disease develops in the small number of infected people whose immune systems do not successfully heal the primary infection. The disease can occur within weeks after the primary infection, or may lie dormant for years before causing illness. Infants, the elderly, and those infected with HIV are at higher risk for the disease worsening, because of their weaker immune systems. In disseminated disease, organs and tissues affected can include: - Bones and joints
- Bronchus
- Cervical lymph nodes
- Eye
- Larynx (voice box)
- Lining of the abdominal cavity (peritoneum)
- Lining of the brain and spinal cord (meninges)
- Lining of the heart (pericardium)
- Organs of the male or female urinary and reproductive systems
- Skin
- Small bowel
- Stomach
The risk of contracting TB increases among those who are in contact with people who have the disease, who live in crowded or unsanitary living conditions, and who have poor nutrition. An increased incidence of TB has been seen recently in the U.S. Factors that may be causing this increase are tuberculosis infections in people with AIDS and HIV, and increasing numbers of homeless people. Another matter of concern is the development of drug-resistant strains of TB. Incomplete treatment of TB infections (such as not taking medications for the prescribed length of time) can contribute to drug-resistant strains of bacteria. About half of AIDS patients with a CD4 count less than 200 who develop TB will have disseminated disease (not localized disease, as in pulmonary tuberculosis). | 
Infectious Diseases 
