Tuberculosis (Pulmonary) - Adult

1. Clinical Overview

Pulmonary Tuberculosis (TB) is a chronic, granulomatous infectious disease caused by the acid-fast bacillus Mycobacterium tuberculosis. It remains one of the world's most significant infectious disease threats, ranking as the leading cause of death from a single infectious agent (surpassing HIV/AIDS) until the COVID-19 pandemic. [1]

TB affects primarily the lung parenchyma but has the biological capacity to disseminate to virtually every organ system in the body, resulting in extrapulmonary TB. The disease manifests along a clinical spectrum from asymptomatic latent infection to life-threatening disseminated disease.

Clinical Spectrum

The disease exists in two fundamental states:

1. Latent Tuberculosis Infection (LTBI):

   • Contained infection with viable but dormant bacilli
   • Completely asymptomatic
   • Non-infectious to others
   • Positive immunological tests (IGRA/Mantoux)
   • Normal chest radiograph
   • 5-10% lifetime risk of progression to active disease [2]

2. Active TB Disease:

   • Failure of immune containment with bacterial proliferation
   • Symptomatic with constitutional and respiratory features
   • Infectious (especially smear-positive pulmonary TB)
   • Radiological abnormalities
   • Requires urgent treatment

Clinical Pearl:

The "Slow Burn" Phenomenon: TB is the quintessential chronic infection. Unlike bacterial pneumonia which declares itself within days, TB typically presents over weeks to months. The classic triad is prolonged fever + drenching night sweats + unintentional weight loss. Always inquire about night sweats that require changing bedclothes—this is a high-specificity clinical feature.

Global Significance

TB represents a critical intersection of infectious disease, public health, and social medicine. The World Health Organization (WHO) estimates:

• 10.6 million new cases annually
• 1.3 million deaths per year
• One-quarter of the global population harbours latent TB infection [1]

The emergence of multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) poses a severe threat to TB control programs worldwide, with cure rates dropping from > 95% for drug-susceptible disease to less than 60% for drug-resistant forms.

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2. Epidemiology

Global Burden

Tuberculosis distribution is markedly heterogeneous across the globe, with distinct geographic and socioeconomic patterns.

Data source: WHO Global Tuberculosis Report 2023 [1]

High-Risk Populations

Certain populations bear a disproportionate burden of TB disease:

Immunocompromised States:

• HIV Co-infection: 18-fold increased risk of developing active TB; leading cause of death in HIV-positive individuals [3]
• Immunosuppressive Medications: Anti-TNF biologics (50-250 fold increased risk), long-term corticosteroids, chemotherapy
• Organ Transplant Recipients: Chronic immunosuppression

Medical Comorbidities:

• Diabetes Mellitus: 2-3 fold increased risk; accounts for 15% of TB cases globally [4]
• Chronic Kidney Disease: Especially end-stage renal disease on dialysis (10-25 fold increased risk)
• Silicosis: 30-fold increased risk
• Gastrectomy/Jejuno-ileal Bypass: Malabsorption states

Social Determinants:

• Poverty and Malnutrition: Body Mass Index less than 18.5 doubles risk
• Homelessness: 35-fold higher incidence in rough sleepers
• Incarceration: Prevalence 10-100 times higher than general population
• Migration: Individuals from high-burden countries
• Healthcare Workers: Occupational exposure risk
• Close Contacts: 5-15% of household contacts develop active TB within first year

Substance Use:

• Tobacco Smoking: Doubles risk of TB infection and disease
• Alcohol Use Disorder: 3-fold increased risk
• Injection Drug Use: Associated with higher transmission rates

UK Epidemiology

In the United Kingdom:

• Annual incidence: 8.3 per 100,000 (declining trend)
• 70% of cases occur in non-UK born individuals
• Highest rates: London boroughs, West Midlands
• Age distribution: Bimodal (young adults 15-44 years; elderly > 65 years)
• Drug resistance: MDR-TB accounts for 1.6% of cases

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3. Aetiology and Pathophysiology

Microbiology of Mycobacterium tuberculosis

Exam Detail: Taxonomic Classification:

• Kingdom: Bacteria
• Phylum: Actinobacteria
• Order: Mycobacteriales
• Family: Mycobacteriaceae
• Genus: Mycobacterium
• Species: M. tuberculosis complex (includes M. tuberculosis, M. bovis, M. africanum, M. microti)

Microbiological Characteristics:

1. Cell Wall Structure:

   • Exceptionally thick, lipid-rich cell wall (60% lipid content)
   • High concentration of mycolic acids (long-chain fatty acids unique to mycobacteria)
   • Arabinogalactan-peptidoglycan complex
   • Outer capsular layer containing glycolipids

2. Acid-Fast Property:

   • Retains carbolfuchsin dye despite acid-alcohol decolorization
   • Due to mycolic acid impermeability
   • Diagnostic basis for Ziehl-Neelsen (ZN) and Auramine-Rhodamine staining
   • Does NOT Gram stain effectively ("Gram-neutral")

3. Aerobic Metabolism:

   • Obligate aerobe requiring high oxygen tension
   • Explains predilection for pulmonary apices (highest PO₂)
   • Thrives in well-oxygenated upper lung zones
   • Dormant in hypoxic, acidic granuloma centres (latent TB)

4. Growth Characteristics:

   • Extremely slow generation time: 15-20 hours (vs. 20 minutes for E. coli)
   • Requires specialized culture media (Löwenstein-Jensen, Middlebrook 7H10/7H11)
   • Visible colonies: 3-8 weeks on solid media
   • Liquid culture (MGIT - Mycobacteria Growth Indicator Tube): 10-14 days
   • Non-motile, non-spore-forming

5. Virulence Factors:

   • Cord Factor (Trehalose Dimycolate): Induces granuloma formation, inhibits neutrophil migration
   • Lipoarabinomannan (LAM): Immunomodulatory, prevents phagosome-lysosome fusion
   • Catalase-Peroxidase (KatG): Detoxifies reactive oxygen species
   • ESAT-6 and CFP-10: Early secreted antigens; targets of IGRA tests

Transmission Dynamics

Route: Airborne transmission via droplet nuclei

Infectious Particle Characteristics:

• Particle size: less than 5 micrometres (evaporated respiratory droplets)
• Generated by coughing, sneezing, talking, singing
• Remain suspended in air for hours
• Reach terminal alveoli, evading mucociliary clearance
• Each cough generates ~3,000 droplet nuclei

Infectiousness Determinants:

• Smear-positive pulmonary TB: Highly infectious (> 10,000 bacilli/mL sputum)
• Smear-negative, culture-positive TB: Low infectiousness
• Extrapulmonary TB: Generally non-infectious (exception: laryngeal TB)
• Cavitary disease: Maximum bacillary load and infectivity
• Duration of exposure: Prolonged close contact increases transmission risk

Transmission Risk:

• Only ~30% of close contacts become infected (positive IGRA/Mantoux)
• Of infected individuals, only 5-10% develop active disease
• Greatest risk: First 2 years post-infection

Pathophysiological Timeline

Stage 1: Initial Infection and Primary TB (Ghon Complex)

Weeks 0-3:

1. Inhalation: Droplet nuclei containing 1-3 bacilli reach alveoli
2. Alveolar Macrophage Phagocytosis:
   • Bacilli engulfed by alveolar macrophages via mannose receptors
   • Bacilli resist killing within phagosome (prevent lysosome fusion)
   • Intracellular replication begins (unchecked for 2-3 weeks)
3. Local Spread:
   • Infected macrophages transport bacilli to regional hilar lymph nodes
   • Haematogenous dissemination to distant organs (often subclinical)

Weeks 3-8:

4. Cell-Mediated Immunity Activation:

   • Antigen presentation via MHC Class II to CD4+ T cells
   • Th1 response: IFN-γ and TNF-α production
   • Macrophage activation into epithelioid histiocytes
   • Granuloma Formation: Central caseous necrosis surrounded by epithelioid macrophages, Langhans giant cells, lymphocytes, fibroblasts

5. Ghon Complex Development:

   • Ghon Focus: Primary parenchymal granuloma (typically mid/lower zones)
   • Lymphangitis: Lymphatic involvement
   • Hilar Lymphadenopathy: Draining node granulomas
   • Ghon Focus + Hilar Nodes = Ghon Complex

Outcome in Immunocompetent Host (90%):

• Immune containment
• Granuloma calcification (visible on CXR as Ranke Complex)
• Transition to latent TB infection

Outcome in Immunocompromised/Children (10%):

• Progressive Primary TB: Unchecked progression to active disease
• Miliary TB: Haematogenous dissemination (millet seed pattern on imaging)
• TB Meningitis: Especially in young children

Stage 2: Latent Tuberculosis Infection (LTBI)

Immunological Stalemate:

• Viable but dormant bacilli sequestered within granulomas
• Hypoxic, acidic, nutrient-poor microenvironment induces bacterial dormancy
• T-cell mediated immunity maintains containment
• Positive tuberculin skin test (TST) or Interferon-Gamma Release Assay (IGRA)
• No clinical or radiological evidence of active disease
• Non-infectious

Duration:

• Can persist for lifetime
• Estimated 5-10% lifetime reactivation risk (half within first 5 years) [2]

Stage 3: Reactivation TB (Post-Primary TB)

Triggers for Reactivation:

• Immunosenescence (aging)
• HIV infection (CD4 count less than 350 cells/μL)
• Immunosuppressive medications
• Malnutrition
• Chronic diseases (diabetes, CKD, malignancy)

Molecular Events:

1. Granuloma Breakdown:

   • Loss of immune surveillance
   • Caseous centre liquefaction
   • Oxygen ingress creates favourable aerobic environment
   • Explosive bacterial replication (10⁷-10⁹ bacilli)

2. Cavity Formation:

   • Liquefied caseum erodes into bronchus
   • Contents expelled via airways (patient becomes infectious)
   • Cavity wall: Fibrotic, poorly vascularized
   • Predilection for apical/posterior segments of upper lobes (highest PO₂)

3. Bronchogenic Spread:

   • Bacilli disseminate via airways to other lung segments
   • "Tree-in-bud" pattern on CT (endobronchial spread)

Anatomical Predilection:

Upper lobe preference explained by:

• Higher oxygen tension (obligate aerobe)
• Less mechanical clearance (impaired lymphatic drainage)
• Preferential ventilation in upright position

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4. Clinical Assessment

History

Tuberculosis presents with a constellation of constitutional, respiratory, and occasionally systemic features. The key clinical feature is chronicity—symptoms evolve over weeks to months.

Constitutional Symptoms ("The Wasting Disease")

1. Fever:

   • Low-grade (37.5-38.5°C)
   • Classically evening pyrexia (temperature rises in afternoon/evening)
   • Rarely high-grade unless miliary/disseminated TB
   • Duration: Typically > 2-3 weeks

2. Night Sweats:

   • "Drenching" quality: Severe enough to require changing bedclothes/nightwear
   • High specificity for TB when present
   • May wake patient from sleep

3. Weight Loss:

   • Unintentional
   • Often > 5% body weight
   • Accompanied by anorexia
   • Historical term "consumption" derives from this wasting

4. Fatigue:

   • Profound tiredness disproportionate to activity
   • Progressive functional impairment

Respiratory Symptoms

1. Cough:

   • Duration > 2-3 weeks (WHO screening criterion)
   • Initially dry, becomes productive
   • Purulent or mucopurulent sputum

2. Haemoptysis:

   • Blood-streaked sputum (common)
   • Frank haemoptysis (suggests cavitary disease)
   • Massive haemoptysis (> 500 mL/24h): Rasmussen's aneurysm rupture—MEDICAL EMERGENCY

3. Dyspnoea:

   • Uncommon in uncomplicated pulmonary TB
   • Suggests extensive disease, pleural effusion, or pneumothorax

4. Chest Pain:

   • Pleuritic pain indicates pleural involvement
   • Dull ache may occur with cavitation

Exposure and Risk Assessment

Critical History Points:

• TB Contact History: Known TB case exposure (household, workplace)
• Migration History: Birth/residence in high-burden country
• Previous TB: Prior treatment, adherence, outcomes
• HIV Status: Test all TB patients
• Immunosuppression: Medications (anti-TNF, steroids), transplant, chemotherapy
• Comorbidities: Diabetes, CKD, silicosis
• Social History: Homelessness, incarceration, substance use
• Occupational History: Healthcare worker, laboratory staff
• BCG Vaccination: Protective against severe childhood TB (not reliable for adult pulmonary TB)

Physical Examination

Important Note: Physical signs are often subtle or absent in early pulmonary TB. A normal examination does NOT exclude TB.

General Inspection

• Cachexia: Wasting, temporal wasting
• Pallor: Anaemia of chronic disease
• Lymphadenopathy: Cervical nodes (scrofula—TB lymphadenitis)
  • Matted, painless, may have "collar-stud" abscess
• Clubbing: Rare; late sign of extensive disease

Respiratory Examination

Inspection:

• Respiratory rate: Usually normal unless extensive disease
• Reduced chest expansion: Unilateral if apical fibrosis/pleural disease

Palpation:

• Trachea: May deviate away from pleural effusion, toward fibrosis
• Reduced expansion: Affected side in advanced disease

Percussion:

• Dullness: Pleural effusion, consolidation
• Hyperresonance: Pneumothorax (complication)

Auscultation:

• Apical crepitations: Classic finding in upper lobe disease
• Post-tussive crackles: Heard after patient coughs
• Bronchial breathing: Consolidation or cavitation (amphoric quality in large cavities)
• Reduced breath sounds: Pleural effusion, pneumothorax
• Pleural rub: Tuberculous pleuritis

Extrapulmonary Signs ("Beyond the Lungs")

Lymph Nodes:

• Cervical, supraclavicular adenopathy (TB lymphadenitis)
• Painless, matted, may form cold abscess

Musculoskeletal:

• Spine (Pott's Disease):
  • Gibbus deformity (angular kyphosis)
  • Vertebral tenderness
  • Neurological signs (cord compression)
• Large joints: TB arthritis (knee, hip)

Abdominal:

• Ascites (TB peritonitis—dough-like consistency)
• Hepatosplenomegaly (miliary TB)

Neurological:

• Meningism (TB meningitis—neck stiffness, photophobia)
• Cranial nerve palsies (basal meningitis)
• Focal deficits (tuberculoma)

Cardiovascular:

• Muffled heart sounds, pericardial rub (TB pericarditis)
• Signs of tamponade or constriction

Clinical Patterns and Presentations

Exam Detail: Classical Reactivation TB:

• Middle-aged/elderly patient
• Gradual onset over months
• Constitutional symptoms prominent
• Apical lung involvement
• Cavitation on imaging

HIV-Associated TB:

• Younger patient
• Atypical presentation (may lack classic symptoms)
• Lower lobe predominance (impaired immunity fails to wall off infection)
• Miliary pattern common
• Minimal cavitation (insufficient immune response)
• Extrapulmonary involvement frequent
• May have normal CXR in 10-15% (especially if CD4 less than 200)

Primary Progressive TB (Children/Immunosuppressed):

• Acute/subacute presentation
• Marked lymphadenopathy
• Middle/lower lobe consolidation
• Pleural effusion
• Rapid progression risk

Miliary TB ("Cryptic Disseminated TB"):

• Fever of unknown origin
• Multi-organ failure
• Minimal respiratory symptoms initially
• Diffuse micronodular pattern on CXR
• High mortality if unrecognized

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5. Differential Diagnosis

The chronic nature and varied presentations of TB create a broad differential diagnosis.

Key Differentials with Comparison

Specific Differential Considerations

Infectious:

• Bacterial Pneumonia: Acute onset, lobar consolidation, responds to standard antibiotics
• Atypical Pneumonia: Mycoplasma, Legionella—subacute but shorter duration than TB
• Fungal Pneumonia:
  • "Aspergillus: Cavitary disease, aspergilloma in old TB cavities"
  • "Histoplasma: Endemic areas, mimics TB radiologically"
  • "Coccidioides: Southwestern US, cavitation similar to TB"
• Nontuberculous Mycobacteria (NTM):
  • M. avium complex, M. kansasii
  • Indolent course, cavitation, difficult to distinguish
  • Requires culture speciation

Malignancy:

• Lung Cancer:
  • "Squamous cell: Upper lobe, cavitation"
  • Weight loss, haemoptysis overlap
  • Requires tissue diagnosis
• Lymphoma: Mediastinal lymphadenopathy, B symptoms

Inflammatory:

• Sarcoidosis:
  • Bilateral hilar lymphadenopathy (stage I)
  • Upper lobe fibrosis (stage IV)
  • Non-caseating granulomas
• Wegener's Granulomatosis (GPA): Cavitating nodules, systemic vasculitis
• Organizing Pneumonia: Migratory infiltrates

Other:

• Bronchiectasis: Chronic productive cough, recurrent infections
• Lung Abscess: Acute, foul-smelling sputum, air-fluid level
• Pulmonary Embolism with Infarction: Acute dyspnoea, pleuritic pain

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6. Investigations

Diagnostic Algorithm

graph TD
    A[Suspected Pulmonary TB] --> B{Collect 2-3 Sputum Samples}
    B --> C[Sputum Smear Microscopy - AFB]
    B --> D[GeneXpert MTB/RIF NAAT]
    B --> E[Sputum Culture]
    
    C --> F{Smear Positive?}
    F -->|Yes| G[Highly Infectious - Isolate]
    F -->|No| H[Smear-Negative TB Possible]
    
    D --> I{MTB Detected?}
    I -->|MTB Detected, Rif Sensitive| J[Start Standard RIPE Therapy]
    I -->|MTB Detected, Rif Resistant| K[Refer for MDR-TB Regimen]
    I -->|MTB Not Detected| L[Consider Alternative Diagnosis or Clinical TB]
    
    E --> M[Definitive Diagnosis + Full DST]
    M --> N{Culture Positive?}
    N -->|Yes| O[Confirm Species, Drug Susceptibility]
    N -->|No| P[Clinical TB if High Suspicion]
    
    H --> Q[Clinical + Radiological Assessment]
    Q --> R{High Clinical Suspicion?}
    R -->|Yes| S[Empirical TB Treatment]
    R -->|No| T[Investigate Differentials]

Microbiological Investigations

1. Sputum Smear Microscopy (Ziehl-Neelsen or Auramine Stain)

Principle: Detects acid-fast bacilli (AFB)

Procedure:

• Collect 3 sputum samples (spot-morning-spot or spot-spot-spot)
• Early morning specimen preferred (highest yield)
• Ziehl-Neelsen stain (carbolfuchsin) or Auramine-Rhodamine (fluorescence)

Interpretation:

Grading System (WHO):

• 3+: > 10 AFB per field
• 2+: 1-10 AFB per field
• 1+: 10-99 AFB per 100 fields
• Scanty: less than 10 AFB per 100 fields

Sensitivity: 50-60% (requires 5,000-10,000 bacilli/mL) Specificity: High (but cannot distinguish M. tuberculosis from NTM) Time: less than 24 hours

2. Nucleic Acid Amplification Test (NAAT) - GeneXpert MTB/RIF

Gold Standard Initial Test (WHO recommendation) [5]

Principle:

• Real-time PCR detection of M. tuberculosis DNA
• Simultaneous detection of rifampicin resistance (rpoB gene mutations)

Advantages:

• High sensitivity: 90-95% (smear-positive); 70-75% (smear-negative)
• High specificity: > 98%
• Rapid: Results in 2 hours
• Detects rifampicin resistance (marker for MDR-TB)

Sample Types:

• Sputum (induced if non-productive)
• Bronchial washings
• Pleural fluid, CSF, lymph node aspirate (extrapulmonary TB)

Interpretation:

Limitations:

• Cannot distinguish viable from dead bacilli (may remain positive post-treatment)
• Does not provide full drug susceptibility profile
• Cannot detect resistance to isoniazid, pyrazinamide, ethambutol alone

3. Mycobacterial Culture (Gold Standard for Diagnosis)

Principle: Growth and isolation of M. tuberculosis

Media Types:

• Solid media: Löwenstein-Jensen (LJ), Middlebrook 7H10/7H11
  • "Time to result: 3-8 weeks"
• Liquid media: MGIT (Mycobacteria Growth Indicator Tube)
  • "Time to result: 10-21 days"
  • Higher sensitivity, faster

Advantages:

• 100% specificity (allows species identification)
• Drug Susceptibility Testing (DST): Full profile for first-line and second-line drugs
• Highest sensitivity: Detects less than 100 bacilli/mL

Drug Susceptibility Testing (DST):

• Phenotypic: Tests bacterial growth in presence of drugs
• First-line drugs: Rifampicin, isoniazid, pyrazinamide, ethambutol
• Second-line drugs: Fluoroquinolones, aminoglycosides, bedaquiline, linezolid

Genotypic DST:

• Line probe assays (LPA): Detects resistance mutations
• Rapid results (1-2 days)

Limitations:

• Time delay (weeks)
• Requires biosafety level 3 laboratory

4. Alternative Rapid Tests

Urine Lipoarabinomannan (LAM) Lateral Flow Assay:

• Detects mycobacterial LAM antigen in urine
• Indication: HIV-positive patients with CD4 less than 200 cells/μL or seriously ill
• Point-of-care test (20 minutes)
• Sensitivity: 40-60% (higher in advanced HIV)
• Specificity: 85-95%

Limitation: Only validated in HIV-positive patients; poor sensitivity in HIV-negative

Imaging

Chest Radiograph (CXR)

Active Pulmonary TB - Classic Findings:

1. Upper Lobe Predominance:

   • Apical and posterior segments of upper lobes
   • Superior segments of lower lobes

2. Consolidation:

   • Patchy, heterogeneous opacities
   • Poorly defined margins

3. Cavitation:

   • Thick-walled cavities
   • Air-fluid levels (if superinfected)
   • Single or multiple
   • Strongest predictor of smear-positivity

4. Nodules:

   • Poorly defined
   • May coalesce

5. Pleural Effusion:

   • Unilateral (usually)
   • Exudative, lymphocytic

6. Lymphadenopathy:

   • Hilar or mediastinal
   • More common in primary TB and HIV

Miliary TB:

• Diffuse, bilateral 1-3 mm micronodules ("millet seed" pattern)
• Uniform distribution throughout both lungs
• Represents haematogenous dissemination

Old/Healed TB:

• Apical fibrosis
• Calcified granulomas (Ghon focus, Ranke complex)
• Volume loss (upper lobe retraction)
• Bronchiectasis (traction)

CXR Limitations:

• 10-15% of active TB has normal CXR (especially HIV-positive with low CD4)
• Cannot distinguish active from old TB (requires microbiological confirmation)

Computed Tomography (CT) Chest

Indications:

• Smear-negative/culture-negative suspected TB
• Assessment of disease extent
• Evaluation of complications
• Difficult differential diagnosis

Additional Features Detected:

• Tree-in-bud pattern: Small centrilobular nodules with branching linear opacities (endobronchial spread)
• Cavitation: More sensitive than CXR
• Bronchiectasis
• Mediastinal lymphadenopathy: Central necrosis (low attenuation)

Immunological Tests for Latent TB

Critical: These tests detect LTBI (not active TB). DO NOT use to diagnose active disease.

Tuberculin Skin Test (TST / Mantoux Test)

Principle: Type IV hypersensitivity reaction to tuberculin PPD (purified protein derivative)

Procedure:

• Intradermal injection of 0.1 mL tuberculin (5 TU PPD) on volar forearm
• Read induration (NOT erythema) at 48-72 hours

Interpretation (Induration Diameter):

False Positives:

• BCG vaccination (especially if given after infancy)
• NTM exposure
• Incorrect administration/reading

False Negatives:

• Anergy (severe immunosuppression, HIV, malnutrition)
• Recent TB infection (less than 8 weeks)
• Very old age
• Overwhelming TB disease (miliary)
• Recent live virus vaccination (measles, MMR)

Interferon-Gamma Release Assay (IGRA)

Commercial Tests:

• QuantiFERON-TB Gold Plus
• T-SPOT.TB

Principle:

• Blood test measuring IFN-γ release from T-cells in response to TB-specific antigens (ESAT-6, CFP-10, TB7.7)

Advantages over TST:

• NOT affected by BCG vaccination
• Single visit (no need for return reading)
• Less cross-reactivity with NTM
• Objective: No reader variability

Interpretation:

Limitations:

• Cannot distinguish LTBI from active TB
• Expensive
• Requires laboratory infrastructure
• False negatives in immunosuppression

UK Guidance:

• IGRA preferred in BCG-vaccinated individuals
• TST acceptable if IGRA unavailable

Histopathology

Indication: Extrapulmonary TB, tissue diagnosis when sputum unavailable

Classic Finding:

• Caseating granulomas:
  • Central caseous (cheese-like) necrosis
  • Epithelioid macrophages
  • Langhans giant cells (horseshoe nuclei)
  • Lymphocytic cuff
  • Fibroblasts

Special Stains:

• Ziehl-Neelsen or Auramine stains may reveal AFB within granuloma

Differential: Sarcoidosis (non-caseating granulomas), fungal infection

Baseline Investigations Before Treatment

Before initiating TB therapy, obtain:

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7. Classification

Clinical Classification

Drug Resistance Classification [6]

Global Burden:

• MDR/RR-TB: ~450,000 cases annually (3.4% of new cases; 18% of retreatment cases)
• XDR-TB: ~6% of MDR-TB cases

Risk Factors for Drug Resistance:

• Previous TB treatment
• Contact with known MDR-TB case
• HIV infection
• Birth/residence in high MDR-TB burden countries (Eastern Europe, Asia)

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8. Management

Guiding Principles

1. Cure the patient
2. Prevent death and disability
3. Prevent transmission
4. Prevent drug resistance (requires adherence to full course)

Treatment of active TB is standardized globally and based on WHO guidelines. [7]

Standard Regimen for Drug-Susceptible TB

"RIPE" Therapy: Total duration 6 months

Intensive Phase (2 months): Rifampicin + Isoniazid + Pyrazinamide + Ethambutol
Continuation Phase (4 months): Rifampicin + Isoniazid

Notation: 2HRZE/4HR

Rationale for 4-Drug Intensive Phase:

• Isoniazid + Rifampicin: Backbone; bactericidal
• Pyrazinamide: Active against semi-dormant bacilli in acidic environment; sterilizing
• Ethambutol: Added as 4th drug to prevent resistance if unrecognized INH resistance exists

Why 6 Months?

• Kills actively dividing bacilli (days-weeks)
• Eradicates semi-dormant bacilli in acidic/hypoxic environments (months)
• Prevents relapse

Drug Dosing (Adult)

Fixed-Dose Combinations (FDC):

• Preferred to improve adherence and reduce prescribing errors
• Example: Rifater (RIF+INH+PZA), Rifinah (RIF+INH)

Drug Mechanisms and Toxicity

Exam Detail: | Drug | Mechanism of Action | Key Side Effects | Monitoring | Management of Toxicity | |:-----|:--------------------|:-----------------|:-----------|:-----------------------| | Rifampicin | RNA polymerase inhibitor (binds β-subunit) | • Red/orange urine, tears, sweat (HARMLESS—warn patient)
• Hepatotoxicity
• CYP450 inducer (drug interactions)
• Thrombocytopenia
• Flu-like syndrome (intermittent dosing) | LFTs (baseline, 2 weeks, monthly if abnormal) | • Stop if ALT > 3× ULN + symptoms OR > 5× ULN
• Warn: OCP failure (use barrier contraception)
• Adjust warfarin, antiretrovirals | | Isoniazid | Inhibits mycolic acid synthesis (InhA enzyme) | • Peripheral neuropathy (dose-dependent)
• Hepatotoxicity
• Lupus-like syndrome
• Seizures (rare) | LFTs
Neurological symptoms | • PREVENT neuropathy: Co-prescribe Pyridoxine (Vit B6) 10-25 mg daily
• Stop if hepatotoxicity | | Pyrazinamide | Disrupts membrane energetics (acidic pH) | • Hepatotoxicity
• Hyperuricemia/Gout
• Arthralgia | LFTs
Uric acid | • Stop if hepatotoxicity
• Treat gout (NSAIDs; avoid allopurinol during acute attack) | | Ethambutol | Inhibits arabinosyl transferase (cell wall) | • Optic neuritis (retrobulbar)
- Reduced visual acuity
- Red-green colour blindness
- Bilateral
- Dose/duration-dependent | Visual acuity + Ishihara colour vision
Baseline, then monthly | • Stop immediately if vision changes
• Usually reversible if caught early
• May be irreversible if prolonged |

Drug-Induced Hepatotoxicity (Most Important Toxicity)

Drugs: Rifampicin, isoniazid, pyrazinamide (all hepatotoxic)

Definition:

• ALT > 3× upper limit of normal (ULN) with symptoms (nausea, vomiting, jaundice)
• ALT > 5× ULN without symptoms

Management Algorithm:

graph TD
    A[Hepatotoxicity Suspected] --> B{Check ALT, Bilirubin}
    B --> C{ALT > 3x ULN + Symptoms<br />OR<br />ALT > 5x ULN}
    C -->|Yes| D[STOP ALL TB DRUGS IMMEDIATELY]
    C -->|No| E[Continue treatment; monitor closely]
    
    D --> F[Supportive Care]
    F --> G{Liver Enzymes Normalizing?}
    G -->|Yes| H[Sequential Re-introduction]
    G -->|No| I[Alternative Regimen<br />Fluoroquinolone + Ethambutol + Injectable]
    
    H --> J[Re-introduce ONE drug at a time<br />Start with Rifampicin, then Isoniazid]
    J --> K{Monitor LFTs 3-7 days after each drug}
    K -->|Normal| L[Add next drug]
    K -->|Elevated| M[Identify culprit; modify regimen]

Re-introduction Sequence:

1. Rifampicin (most important, least hepatotoxic)
2. Isoniazid
3. Pyrazinamide (most hepatotoxic; may omit and extend continuation phase)

Special Regimens

CNS Tuberculosis (TB Meningitis, Tuberculoma)

• Standard regimen PLUS adjunctive corticosteroids
• Duration: 12 months (2HRZE/10HR)
• Steroids:
  • "Dexamethasone (adults): 8-12 mg daily, taper over 6-8 weeks"
  • OR Prednisolone 60 mg daily, taper

Pregnancy and Breastfeeding

Safe Drugs:

• Rifampicin ✓
• Isoniazid ✓ (+ Pyridoxine)
• Ethambutol ✓

Controversial:

• Pyrazinamide: WHO considers safe; US guidelines more conservative

Contraindicated:

• Streptomycin: Ototoxicity to fetus
• Aminoglycosides: Ototoxicity

Breastfeeding: All first-line drugs safe (minimal milk excretion; insufficient to treat infant)

Renal Impairment

Dose Adjustment Required:

• Ethambutol: Reduce dose; monitor levels
• Pyrazinamide: Reduce dose
• Aminoglycosides: Avoid or dose adjust

No adjustment:

• Rifampicin
• Isoniazid

HIV Co-Infection [8]

TB Treatment:

• Same regimen (2HRZE/4HR)
• Daily dosing preferred (not intermittent)

ART Timing:

• CD4 less than 50: Start ART within 2 weeks of TB treatment
• CD4 50-200: Start ART within 8 weeks
• CD4 > 200: Start ART within 8-12 weeks
• TB Meningitis: Delay ART to 8 weeks (reduce IRIS risk)

Drug Interactions:

• Rifampicin induces CYP450 → reduces ART levels
• Preferred ART:
  • Efavirenz-based (EFV + 2 NRTIs)
  • Dolutegravir 50 mg BD (increased dose due to rifampicin)
• Avoid: Protease inhibitors (levels reduced by rifampicin)

Immune Reconstitution Inflammatory Syndrome (IRIS):

• Paradoxical worsening after ART initiation (2-8 weeks)
• Due to immune recovery
• Presents: New/worsening lymphadenopathy, fever, CNS lesions
• Management: Continue TB/ART; add corticosteroids if severe

Treatment Monitoring

Microbiological Response:

Treatment Failure:

• Smear/culture positive at Month 5
• Investigate: Adherence, drug resistance, malabsorption, wrong diagnosis

Follow-up Post-Treatment:

• Clinical review at 12 and 24 months
• Educate on relapse symptoms

Directly Observed Therapy (DOT / DOTS)

WHO Strategy: Healthcare worker or trained volunteer watches patient swallow each dose

Indications (Strong Recommendation):

• All patients (ideally)
• Especially: Drug resistance, homelessness, substance use, prior non-adherence, HIV

Benefits:

• Improved adherence
• Reduced relapse
• Reduced acquired drug resistance
• Early detection of adverse effects

Management of MDR-TB / RR-TB [6]

Definition: Resistance to rifampicin ± isoniazid

Treatment Principles:

• Longer duration: 18-24 months
• Second-line drugs (more toxic, less effective)
• Expert consultation required

WHO Recommended Regimen (All-Oral, Shorter):

• Bedaquiline + Pretomanid + Linezolid (BPaL regimen) for 6-9 months (selected patients)
• OR longer regimen (18-24 months):
  • Bedaquiline, Linezolid, Fluoroquinolone (Levofloxacin/Moxifloxacin), Cycloserine, Clofazimine

Group Hierarchy:

• Group A: Levofloxacin/Moxifloxacin, Bedaquiline, Linezolid
• Group B: Cycloserine, Clofazimine, Delamanid
• Group C: Ethambutol, Pyrazinamide, Ethionamide, Aminoglycosides (Amikacin)

Cure Rates: 50-60% (vs. > 95% for drug-susceptible)

Adverse Effects:

• Linezolid: Peripheral neuropathy, bone marrow suppression
• Bedaquiline: QT prolongation
• Fluoroquinolones: Tendonitis, QT prolongation
• Cycloserine: Psychiatric disturbances

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9. Complications

Pulmonary Complications

Extrapulmonary Complications

TB Meningitis:

• Basal meningeal inflammation
• Cranial nerve palsies (III, VI, VII)
• Hydrocephalus, stroke (vasculitis)
• High mortality (20-50%)
• Treatment: 12 months therapy + steroids

Pott's Disease (Spinal TB):

• Vertebral body destruction
• Kyphosis (gibbus deformity)
• Cord compression → paraplegia
• Treatment: Standard TB drugs + surgical decompression if neurology

Constrictive Pericarditis:

• Chronic pericardial inflammation → calcification → constriction
• Right heart failure
• Treatment: Pericardiectomy

Adrenal Insufficiency (Addison's Disease):

• Bilateral adrenal destruction
• Hypotension, hyperpigmentation, electrolyte disturbance
• Treatment: Lifelong steroid replacement

Miliary TB:

• Multi-organ dissemination
• ARDS, hepatosplenomegaly, meningitis
• High mortality if untreated

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10. Prognosis and Prevention

Prognosis

Drug-Susceptible TB:

• Cure rate: > 95% with adherence to 6-month regimen
• Relapse rate: less than 5% if fully treated
• Mortality: less than 1% in immunocompetent; higher in HIV/elderly

Drug-Resistant TB:

• MDR-TB cure rate: 50-60%
• XDR-TB cure rate: 30-40%
• Treatment duration: 18-24 months

Post-TB Lung Disease:

• 50% of survivors have permanent lung impairment (fibrosis, bronchiectasis) despite microbiological cure [9]
• May develop chronic respiratory symptoms

Mortality Risk Factors:

• Advanced age
• HIV co-infection (especially CD4 less than 50)
• Delayed diagnosis
• Drug resistance
• Miliary/CNS TB
• Comorbidities (diabetes, CKD, malnutrition)

Prevention

1. Vaccination

BCG (Bacillus Calmette-Guérin):

• Live attenuated Mycobacterium bovis vaccine
• Efficacy:
  • 70-80% protective against severe childhood TB (meningitis, miliary)
  • Variable efficacy against adult pulmonary TB (0-80%)
• UK Policy: Offered to high-risk neonates and children
• Contraindications: Immunosuppression, HIV, pregnancy

Novel Vaccines in Development:

• M72/AS01E: Phase 2b showed 50% efficacy in preventing active TB in LTBI adults
• Revaccination strategies with BCG or new candidates

2. Treatment of Latent TB (LTBI)

Indication: Reduce reactivation risk in high-risk populations

Who to Treat:

• Close contacts of active TB (especially children)
• HIV-positive (regardless of CD4)
• Starting anti-TNF therapy or other immunosuppression
• Recent conversion (TST/IGRA)
• Silicosis
• Transplant candidates

Regimens:

Contraindications:

• Active TB (must exclude first)
• Pregnancy (for rifampicin-containing regimens—controversial)

3. Infection Control

Healthcare Settings:

Administrative Controls:

• Early identification and isolation of suspected TB
• Rapid diagnostic testing (GeneXpert)

Environmental Controls:

• Negative pressure rooms (air exhausted outside or HEPA filtered)
• Adequate ventilation (≥12 air changes/hour)
• UV germicidal irradiation

Personal Protective Equipment:

• N95 respirators for healthcare workers
• Surgical masks for patients during transport

Isolation Duration:

• Until 3 consecutive sputum smears negative (usually 2 weeks of effective treatment)

4. Contact Tracing

Process:

• Identify all close contacts
• Screen with symptom questionnaire, CXR, IGRA/TST
• Treat active TB or LTBI as appropriate

Priority:

• Household contacts
• Prolonged close contacts
• Immunosuppressed contacts
• Children less than 5 years

5. Public Health Measures

Notification:

• TB is a notifiable disease in most countries
• Mandatory reporting to public health authorities

DOTS Strategy (WHO):

• Political commitment
• Case detection via quality sputum microscopy
• Standardized treatment with DOT
• Drug supply and management
• Monitoring and evaluation

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11. Evidence and Guidelines

Key Guidelines

Landmark Evidence

Diagnostic Advances:

• Boehme et al. (NEJM 2010): GeneXpert MTB/RIF validation study—established rapid molecular diagnosis as standard [5]

Treatment Duration:

• Hong Kong Chest Service (1991): Established 6-month RIPE regimen as standard (non-inferior to 9 months)

Shorter Regimens:

• NEJM Study (2021): 4-month regimen (rifapentine + moxifloxacin) non-inferior to standard 6-month for drug-susceptible TB

MDR-TB:

• Nix-TB Trial (NEJM 2020): Bedaquiline-Pretomanid-Linezolid (BPaL) 6-month regimen for XDR-TB [10]

LTBI Treatment:

• Sterling et al. (NEJM 2011): 3HP regimen (12 doses isoniazid-rifapentine) equivalent to 9H [11]

HIV-TB Co-infection:

• CAMELIA Trial (NEJM 2011): Early ART (2 weeks) in HIV-TB reduces mortality in advanced HIV [8]

---

12. Examination Focus

Viva Questions and Model Answers

Exam Detail: Q1: Why does TB preferentially affect the apices of the lungs?

Model Answer: "Mycobacterium tuberculosis is an obligate aerobe requiring high oxygen tension for replication. The apical and posterior segments of the upper lobes have the highest partial pressure of oxygen due to superior ventilation-perfusion matching in the upright position. Additionally, these areas have relatively impaired lymphatic drainage, allowing bacilli to persist. In primary infection, however, TB affects the mid/lower zones (better perfused in children who spend more time supine). Reactivation TB characteristically involves the apices."

---

Q2: A patient on standard RIPE therapy develops jaundice at 4 weeks. How would you manage this?

Model Answer: "This suggests drug-induced hepatotoxicity, as rifampicin, isoniazid, and pyrazinamide are all hepatotoxic. I would:

1. Immediately check LFTs (ALT, AST, bilirubin) and assess symptom severity
2. If ALT > 3× ULN with symptoms or > 5× ULN without symptoms: STOP ALL TB DRUGS immediately
3. Supportive care and monitor liver function
4. Once LFTs normalizing: Sequential re-introduction of drugs one at a time:
   • Start with Rifampicin (most important, least hepatotoxic)
   • Add Isoniazid after 3-7 days if LFTs stable
   • Consider omitting Pyrazinamide (most hepatotoxic) and extending continuation phase to 7 months (2HRE/7HR)
5. If severe hepatotoxicity persists: Use alternative regimen with fluoroquinolone, ethambutol, and injectable agent"

---

Q3: How does HIV infection alter the presentation and management of tuberculosis?

Model Answer: "HIV-TB co-infection presents several challenges:

Presentation Differences:

• Atypical radiological patterns: Lower lobe predominance, less cavitation, miliary pattern common
• 10-15% have normal CXR (especially if CD4 less than 200)
• Extrapulmonary TB more common (40-50% vs. 15% in HIV-negative)
• Higher smear-negative rate (inadequate immune response to form cavities)

Diagnostic Challenges:

• Lower sensitivity of smear microscopy
• IGRA may be negative (anergy)
• Urine LAM useful in advanced HIV (CD4 less than 200)

Treatment:

• Same TB regimen (2HRZE/4HR) but daily dosing preferred
• ART timing critical:
  • "CD4 less than 50: Start within 2 weeks"
  • "CD4 50-200: Start within 8 weeks"
  • "CD4 > 200: Start within 8-12 weeks"
• Drug interactions: Rifampicin reduces ART levels; use Efavirenz or double-dose Dolutegravir
• IRIS risk: Paradoxical worsening 2-8 weeks after ART; manage with steroids if severe
• Higher mortality: Especially if delayed diagnosis or advanced immunosuppression"

---

Q4: What is the mechanism of action of pyrazinamide, and why is it only given for 2 months?

Model Answer: "Pyrazinamide is a unique sterilizing drug that works specifically in acidic environments (pH 5.5).

Mechanism:

• Converted to pyrazinoic acid by bacterial pyrazinamidase
• Disrupts mycobacterial membrane energetics and ion transport
• Particularly active against semi-dormant bacilli residing in acidic, hypoxic centres of granulomas (where other drugs penetrate poorly)

Duration Rationale:

• Given only in intensive phase (2 months) because it achieves sterilization early
• Key to shortening regimen from 9 months to 6 months
• Hepatotoxicity risk limits prolonged use
• By continuation phase, semi-dormant population eliminated; rifampicin + isoniazid sufficient

Side Effects:

• Hepatotoxicity
• Hyperuricemia/gout (inhibits renal urate excretion)
• Arthralgia"

---

Q5: Describe the pathological evolution of a Ghon complex.

Model Answer: "The Ghon complex represents primary TB infection and evolves through distinct stages:

Initial Infection (Week 0-3):

• Inhaled bacilli reach alveoli
• Phagocytosed by alveolar macrophages but resist killing
• Intracellular replication and local spread

Immune Response (Week 3-8):

• Ghon Focus: Primary parenchymal granuloma forms (typically mid/lower zones in well-perfused areas)
• Granuloma structure: Central caseous necrosis, epithelioid macrophages, Langhans giant cells, lymphocytic rim
• Lymphangitis: Bacilli drain to hilar lymph nodes
• Hilar Lymphadenopathy: Regional node involvement (often more prominent than parenchymal focus)

Ghon Complex = Ghon Focus + Hilar Lymphadenopathy

Resolution (Months):

• In immunocompetent individuals, granulomas undergo dystrophic calcification
• Radiologically visible as calcified nodule + calcified hilar nodes = Ranke Complex
• Bacilli remain viable but dormant (LTBI)

Complications (10% in immunocompromised/children):

• Progressive primary TB
• Erosion into bronchus (endobronchial spread)
• Haematogenous dissemination (miliary TB)
• Lymph node compression (airway obstruction)"

---

Q6: A patient with active pulmonary TB has a positive IGRA. What does this mean?

Model Answer: "This is expected and does NOT provide additional diagnostic value in active TB.

IGRA Interpretation:

• Positive IGRA indicates TB infection (current or past)
• Cannot distinguish:
  • Latent TB from Active TB
  • Recent infection from remote infection
  • Treated from untreated TB

In this case:

• Positive IGRA confirms TB infection (which we already know from active disease diagnosis)
• Active TB is diagnosed via:
  • Clinical presentation
  • Radiological findings
  • Microbiological confirmation (sputum smear, GeneXpert, culture)

IGRA Use:

• Screening for LTBI in asymptomatic individuals
• Contact tracing
• Pre-immunosuppression screening (anti-TNF, transplant)

Bottom Line: Never use IGRA/TST to diagnose active TB—always confirm with microbiology and imaging."

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13. Patient and Layperson Explanation

What is Tuberculosis?

Tuberculosis—often called TB—is an infection caused by bacteria called Mycobacterium tuberculosis. It mainly affects the lungs but can spread to other parts of the body like the bones, brain, or kidneys.

TB is spread through the air when someone with active TB in their lungs coughs or sneezes. Tiny droplets containing the bacteria can be breathed in by others.

Two Types of TB

1. Latent TB (Sleeping TB):

   • The bacteria are in your body but "asleep"
   • You feel completely well
   • You CANNOT spread it to others
   • You need preventive medicine to stop it waking up

2. Active TB (Disease):

   • The bacteria are "awake" and multiplying
   • You feel unwell with symptoms
   • You CAN spread it to others (if in your lungs)
   • You need strong antibiotics for 6 months

Symptoms of Active TB

The most common signs are:

• Cough lasting more than 3 weeks (may have blood)
• Fever (especially in the evening)
• Drenching night sweats (soaking your bedclothes)
• Weight loss without trying
• Feeling very tired

If you have these symptoms, see your doctor urgently.

How is TB Diagnosed?

• Sputum test: You cough up phlegm which is tested for TB bacteria
• Chest X-ray: Pictures of your lungs
• Blood tests: Check your immune response

Treatment

Active TB is treated with 4 different antibiotics for 6 months:

• First 2 months: 4 tablets daily
• Next 4 months: 2 tablets daily

CRITICAL: You MUST take all medicines for the full 6 months, even when you feel better after a few weeks. Stopping early allows the bacteria to become resistant (harder to kill).

Side Effects to Watch For

• Red/orange urine: Normal (from rifampicin)—don't worry
• Yellow eyes or skin (jaundice): STOP tablets and see doctor IMMEDIATELY
• Vision changes: See doctor urgently
• Pins and needles in hands/feet: Tell your doctor

Can TB Be Cured?

Yes! More than 95% of people are completely cured if they take all their medicines correctly for the full 6 months.

Protecting Others

• Cover your mouth when coughing
• In the first 2 weeks of treatment, you may need to stay away from others
• After 2 weeks of treatment, you're much less infectious
• Close family members will be checked for TB

Key Messages

✅ TB is curable with 6 months of antibiotics ✅ Take ALL medicines EVERY DAY for the FULL 6 months ✅ You'll feel better in 2-3 weeks, but bacteria are still there ✅ Stopping early creates "super-bugs" (drug-resistant TB) ✅ Tell your doctor about side effects—medicines can be adjusted

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14. References

1. World Health Organization. Global Tuberculosis Report 2023. Geneva: WHO; 2023. Available at: https://www.who.int/publications/i/item/9789240083851

2. Houben RMGJ, Dodd PJ. The Global Burden of Latent Tuberculosis Infection: A Re-estimation Using Mathematical Modelling. PLoS Med. 2016;13(10):e1002152. DOI: 10.1371/journal.pmed.1002152

3. Getahun H, Gunneberg C, Granich R, Nunn P. HIV Infection-Associated Tuberculosis: The Epidemiology and the Response. Clin Infect Dis. 2010;50(Suppl 3):S201-S207. DOI: 10.1086/651492

4. Jeon CY, Murray MB. Diabetes Mellitus Increases the Risk of Active Tuberculosis: A Systematic Review of 13 Observational Studies. PLoS Med. 2008;5(7):e152. DOI: 10.1371/journal.pmed.0050152

5. Boehme CC, Nabeta P, Hillemann D, et al. Rapid Molecular Detection of Tuberculosis and Rifampin Resistance. N Engl J Med. 2010;363(11):1005-1015. DOI: 10.1056/NEJMoa0907847

6. World Health Organization. WHO Consolidated Guidelines on Drug-Resistant Tuberculosis Treatment. Geneva: WHO; 2019. Available at: https://www.who.int/publications/i/item/9789241550529

7. Nahid P, Dorman SE, Alipanah N, et al. Official American Thoracic Society/Centers for Disease Control and Prevention/Infectious Diseases Society of America Clinical Practice Guidelines: Treatment of Drug-Susceptible Tuberculosis. Clin Infect Dis. 2016;63(7):e147-e195. DOI: 10.1093/cid/ciw376

8. Abdool Karim SS, Naidoo K, Grobler A, et al. Timing of Initiation of Antiretroviral Drugs During Tuberculosis Therapy. N Engl J Med. 2010;362(8):697-706. DOI: 10.1056/NEJMoa0905848

9. Ravimohan S, Kornfeld H, Weissman D, Bisson GP. Tuberculosis and Lung Damage: From Epidemiology to Pathophysiology. Eur Respir Rev. 2018;27(147):170077. DOI: 10.1183/16000617.0077-2017

10. Conradie F, Diacon AH, Ngubane N, et al. Treatment of Highly Drug-Resistant Pulmonary Tuberculosis. N Engl J Med. 2020;382(10):893-902. DOI: 10.1056/NEJMoa1901814

11. Sterling TR, Villarino ME, Borisov AS, et al. Three Months of Rifapentine and Isoniazid for Latent Tuberculosis Infection. N Engl J Med. 2011;365(23):2155-2166. DOI: 10.1056/NEJMoa1104875

12. National Institute for Health and Care Excellence (NICE). Tuberculosis: Prevention, Diagnosis, Management and Service Organisation (NG33). London: NICE; 2016 (updated 2024). Available at: https://www.nice.org.uk/guidance/ng33

13. Sotgiu G, Centis R, D'Ambrosio L, Migliori GB. Tuberculosis Treatment and Drug Regimens. Cold Spring Harb Perspect Med. 2015;5(5):a017822. DOI: 10.1101/cshperspect.a017822

14. Harding E. WHO Global Progress Report on Tuberculosis Elimination. Lancet Respir Med. 2020;8(1):19. DOI: 10.1016/S2213-2600(19)30418-7

15. Lawn SD, Zumla AI. Tuberculosis. Lancet. 2011;378(9785):57-72. DOI: 10.1016/S0140-6736(10)62173-3

16. Migliori GB, Tiberi S, Zumla A, et al. MDR/XDR-TB Management of Patients and Contacts: Challenges Facing the New Decade. The 2020 Clinical Update by the Global Tuberculosis Network. Int J Infect Dis. 2020;92S:S15-S25. DOI: 10.1016/j.ijid.2020.01.042

17. Horsburgh CR Jr, Barry CE 3rd, Lange C. Treatment of Tuberculosis. N Engl J Med. 2015;373(22):2149-2160. DOI: 10.1056/NEJMra1413919

18. Cohen A, Mathiasen VD, Schön T, Wejse C. The Global Prevalence of Latent Tuberculosis: A Systematic Review and Meta-Analysis. Eur Respir J. 2019;54(3):1900655. DOI: 10.1183/13993003.00655-2019

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Document Information:

• Last Updated: 2026-01-07
• Version: 2.0 (Gold Standard)
• Reviewed By: MedVellum Content Team
• Next Review: 2027-01-07