The usual site of the disease is the lungs, but other organs may be involved.
Primary infection is usually asymptomatic .
Pulmonary TB develops in the minority of people whose immune systems do not successfully destroy the primary infection. The disease may occur within weeks after the primary infection or it may lie dormant for years before causing disease. In pulmonary TB, the extent of the disease can vary from minimal to massive involvement, but without effective therapy, the disease becomes progressive. The risk of contracting TB increases with the frequency of contact with people who have the disease, and with crowded or unsanitary living conditions and poor nutrition. Individuals with damaged immune systems from AIDS almost universally develop active tuberculosis upon exposure to the organism.