Inhalation/ingestion/inoculation of mycobacteria is not necessarily followed by infection. Phagocytosis of the mycobacteria by the end-organ macrophages may prevent infection.

If infection does follow, a primary complex ensues with, in the majority, encapsulation of the TB infection. Some mycobacteria may persist in a dormant state. The individual develops a positive tuberculin test.

When and if the immune status of that particular individual is diminished through chronic illness or an overwhelming disease, the scene is set for reactivation (endogenous) or re-infection (exogenous) of TB.

Inactive TB is TB without clinical, radiological or bacterial signs of activity.

Active TB occurs when tuberculosis lesions progress to disease, manifested by progressive radiological changes and the presence of AFB’s (acid fast bacilli) in biological / P.A. (pathological-anatomical) material.