post-primary TB
Post-primary TB is TB that flares up later in life, usually from bacteria left over from an earlier infection that were never fully eliminated. Picture coals banked years ago suddenly catching again when conditions change — most often when the immune system weakens with age, illness or immune-suppressing treatment.
It characteristically affects the upper parts of the lungs, where the higher oxygen levels suit the oxygen-loving bacterium. Here the disease tends to be more destructive than primary TB: it provokes intense inflammation that can break down lung tissue and carve out cavities. Cavities act as bacterial factories that connect to the airways, so cough spreads large numbers of organisms into the air.
Because it is the form that drives most transmission and lung destruction in adults, post-primary TB is what people usually picture as “classic” pulmonary TB. The same disease can occasionally arise not from old bacteria reactivating but from a fresh re-infection in someone who has been exposed before; either way, the upper-lobe, cavitary pattern is typical.
An older adult on long-term steroids develops chronic cough and night sweats; a CT scan shows upper-lobe cavities, and sputum confirms reactivation TB.
Reactivation favouring the upper lobes — the post-primary pattern.
Upper-lobe location and cavitation on imaging are strong clues to post-primary TB, but they are not unique to it and must be confirmed microbiologically.