What is secondary tuberculosis?

Secondary Tuberculosis (Reactivation or Post-primary TB)

Secondary tuberculosis is the form of TB that occurs in a person who has previously been infected with Mycobacterium tuberculosis. It may result from reactivation of latent TB or reinfection with a new strain, usually in the lungs.

Causes

  • Reactivation of dormant bacilli from a previous primary infection (common)

  • Reinfection from external sources (less common, but possible)

Occurs when:

  • Immunity weakens (e.g., HIV, malnutrition, old age, diabetes, immunosuppressive therapy)

Common Sites

  • Apex of the lungs (upper lobes)

    • Higher oxygen tension here favors mycobacterial growth

Pathological Features

Feature Details
Lesion type Caseating granulomas, cavitary lesions
Cavity formation Due to caseous necrosis and tissue destruction
Fibrosis and scarring Seen in chronic cases
Possible spread Local (to other lung areas) or systemic (via blood or lymph)

Clinical Features

Symptom Details
Persistent cough Often productive; may have blood (hemoptysis)
Fever Low-grade, especially in evenings
Night sweats Characteristic feature
Weight loss Marked and unexplained
Chest pain Due to pleural involvement
Fatigue General ill-health

Investigations

  • Chest X-ray: Cavitary lesions, especially in upper lobes

  • Sputum AFB test: Positive in active disease

  • GeneXpert MTB/RIF: Detects TB and rifampicin resistance

  • Mantoux test / IGRA: May be positive but doesn't distinguish active from latent TB

Complications

  • Massive hemoptysis

  • Bronchopleural fistula

  • Miliary TB (hematogenous dissemination)

  • TB meningitis, pericarditis, or bone/joint TB

Primary vs Secondary TB

Feature Primary TB Secondary TB
Occurs in New infection Reactivation or reinfection
Age group Often children Often adults
Site Mid/lower lung zones Apex of lungs
Symptoms Mild or absent Severe and symptomatic
Contagious? Usually not Yes, highly contagious

Summary

  • Secondary TB is usually more severe than primary TB.

  • It occurs due to reactivation of latent bacilli.

  • Affects lung apices, causes cavitation, and is highly contagious.

  • Requires prompt diagnosis and treatment to prevent complications and transmission.


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