Primary tuberculosis.

The natural history of tuberculosis is complex. Primary infection, the initial phase, occurs in people without specific immunity, generally normal children and young adults who have not previously been exposed to Mycobacterium tuberculosis. The initial infection can occur at any time during childhood, but adolescence is the peak time of risk. Primary disease develops within 5 years of the initial infection, which stimulates specific immunity, demonstrated by the development of a positive skin response to purified protein derivative of tuberculin. Although symptoms of primary disease may be few, early detection and treatment are important for both preventing the development of immediate complications, which carry a high risk of morbidity and mortality, and preventing spread of infection following later reactivation of disease. Our understanding of the host's immune response to the primary infection is increasing, and it is hoped this will lead to improved possibilities for vaccines in the future.