Tuberculosis — Diagnosis and Treatment

Tuberculosis (TB) remains one of the leading infectious causes of death worldwide, caused by Mycobacterium tuberculosis complex. Despite being largely preventable and curable, TB infected an estimated 10.6 million people globally in 2022, with 1.3 million deaths. The disease disproportionately affects low- and middle-income countries, with particular burden in sub-Saharan Africa and Southeast Asia.

The pathogenesis of TB involves inhalation of airborne droplets containing viable bacilli. After alveolar deposition, mycobacteria are phagocytosed by alveolar macrophages, where they can survive and multiply due to their unique cell wall composition rich in mycolic acids. This leads to granuloma formation, the hallmark of TB infection. The balance between host immunity and bacterial virulence determines whether infection progresses to active disease or remains latent.

Risk factors for TB progression include:

• HIV co-infection (increases risk 20-fold)
• Immunosuppressive medications (TNF-α inhibitors, corticosteroids)
• Diabetes mellitus
• Malnutrition
• Chronic kidney disease
• Substance abuse (alcohol, tobacco, illicit drugs)
• Age extremes (children <5 years, adults >65 years)
• Recent TB exposure or infection
• Certain genetic factors

Understanding these risk factors is crucial for clinicians to identify patients requiring screening and to implement appropriate preventive measures. The concept of latent versus active TB is fundamental to TB control strategies, as approximately 25% of the global population is estimated to have latent TB infection (LTBI), representing a vast reservoir for future active disease.

Latent tuberculosis infection represents a state where individuals are infected with M. tuberculosis but do not have active disease and are not infectious. LTBI screening is targeted toward high-risk populations rather than universal screening, as recommended by major guidelines including CDC and WHO.

Screening Methods:

1. Tuberculin Skin Test (TST): Uses purified protein derivative (PPD) injected intradermally. Results are read 48-72 hours post-injection by measuring induration diameter. Interpretation varies based on risk factors:

   • ≥5 mm: HIV-positive, recent TB contacts, immunocompromised patients
   • ≥10 mm: Foreign-born from high-prevalence countries, injection drug users, residents of high-risk congregate settings
   • ≥15 mm: Low-risk individuals (if testing indicated)

2. Interferon-Gamma Release Assays (IGRAs): Including QuantiFERON-Gold Plus and T-SPOT.TB, these blood tests measure T-cell response to specific TB antigens (ESAT-6, CFP-10, TB7.7). IGRAs are preferred over TST in BCG-vaccinated individuals and require only one visit.

LTBI Diagnosis Algorithm:

• Positive TST or IGRA
• Normal chest radiograph
• Absence of TB symptoms
• Negative sputum studies (if obtained)

Clinical Vignette 1: A 28-year-old nurse from the Philippines presents for employment screening. She received BCG vaccination as a child and has no symptoms. Chest X-ray is normal. QuantiFERON-Gold Plus is positive.

Discussion: This represents classic LTBI in a healthcare worker from an intermediate TB-burden country. The IGRA is preferred over TST due to prior BCG vaccination. She should receive treatment for LTBI given her healthcare occupation and risk of progression.

Active TB diagnosis requires a combination of clinical, radiological, and microbiological evidence. The approach varies between pulmonary and extrapulmonary TB, with pulmonary TB being more common (85% of cases).

Clinical Presentation:

• Constitutional symptoms: Fever, night sweats, weight loss, anorexia
• Pulmonary symptoms: Persistent cough (>2-3 weeks), hemoptysis, chest pain, dyspnea
• Extrapulmonary manifestations: Depend on site (lymphadenopathy, neurological symptoms, bone pain, etc.)

Diagnostic Workup:

1. Chest Imaging:

   • Chest X-ray: May show upper lobe infiltrates, cavitation, hilar lymphadenopathy, or pleural effusion
   • CT chest: More sensitive for detecting early disease, cavitation, and lymphadenopathy

2. Microbiological Diagnosis:

   • Sputum collection: Minimum 3 specimens, preferably early morning samples
   • Acid-fast bacilli (AFB) smear: Rapid but low sensitivity (45-80%)
   • Nucleic Acid Amplification Tests (NAATs): GeneXpert MTB/RIF Ultra provides rapid diagnosis and rifampin resistance detection within 2 hours
   • Culture: Gold standard with 95% sensitivity but requires 2-8 weeks
   • Drug susceptibility testing: Essential for treatment planning

3. Alternative Specimens:

   • Induced sputum or bronchoscopy with BAL for patients unable to produce sputum
   • Tissue biopsy for extrapulmonary TB
   • Pleural fluid analysis (exudative with lymphocytic predominance)

Diagnostic Algorithm:

WHO-recommended rapid diagnostics include GeneXpert MTB/RIF Ultra as the initial test for adults with signs/symptoms of pulmonary TB, particularly in HIV-endemic settings or where drug resistance is suspected.

Treatment of LTBI aims to prevent progression to active TB and reduce the reservoir of infection in the population. The decision to treat LTBI must balance the risk of progression against potential drug toxicity.

Indications for LTBI Treatment:

• Recent TB contacts (especially household contacts)
• Immunocompromised patients (HIV, transplant recipients, TNF-α inhibitor use)
• Healthcare workers
• Foreign-born from high TB-burden countries (within 5 years of arrival)
• Residents of high-risk congregate settings
• Medical conditions increasing TB risk (diabetes, chronic kidney disease, silicosis)

LTBI Treatment Regimens (2023 Guidelines):

1. Preferred Short-Course Regimens:

   • 3HP: Isoniazid 15 mg/kg + Rifapentine 15-20 mg/kg weekly × 12 weeks
   • 3HR: Isoniazid 5 mg/kg + Rifampin 10 mg/kg daily × 3 months
   • 4R: Rifampin 10 mg/kg daily × 4 months

2. Alternative Regimens:

   • 9H: Isoniazid 5 mg/kg daily × 9 months (historical standard)
   • 6H: Isoniazid 5 mg/kg daily × 6 months (less effective than 9H)

Monitoring During LTBI Treatment:

• Baseline: CBC, comprehensive metabolic panel, liver function tests
• Monthly clinical assessment for symptoms of hepatotoxicity
• Laboratory monitoring only if baseline abnormalities or symptoms develop
• Hepatotoxicity criteria: ALT >3× ULN with symptoms or >5× ULN without symptoms

Contraindications:

• Active liver disease or significantly elevated transaminases
• Previous severe adverse reactions to anti-TB medications
• Pregnancy (rifamycins preferred over isoniazid)

Treatment Completion Criteria:

• 3HP: 11 of 12 doses within 16 weeks
• 3HR: 78 of 90 doses within 4 months
• 4R: 104 of 120 doses within 6 months
• 9H: 252 of 270 doses within 12 months

Active TB treatment follows established principles: multiple drugs to prevent resistance, adequate duration to ensure cure, and directly observed therapy (DOT) when indicated. Treatment is divided into intensive (initial) and continuation phases.

Standard First-Line Treatment (Drug-Susceptible TB):

Intensive Phase (2 months): HRZE

• Isoniazid (H): 5 mg/kg daily (max 300 mg)
• Rifampin (R): 10 mg/kg daily (max 600 mg)
• Ethambutol (E): 15-20 mg/kg daily (max 1600 mg)
• Pyrazinamide (Z): 20-25 mg/kg daily (max 2000 mg)

Continuation Phase (4 months): HR

• Isoniazid and Rifampin at same doses
• Total treatment duration: 6 months for pulmonary TB
• Extended treatment (9-12 months) for TB meningitis, bone/joint TB, or cavitary disease with positive 2-month cultures

Alternative Regimens:

• Intermittent therapy: 3 times weekly dosing with higher doses (DOT required)
• Fixed-dose combinations: Improve adherence and reduce prescription errors

Monitoring Active TB Treatment:

Treatment Response Monitoring:

• Clinical improvement: Fever resolution within 2 weeks, weight gain, symptom improvement
• Radiological improvement: May lag clinical improvement by months
• Microbiological response:
  • AFB smear conversion: 85% negative by 2 months
  • Culture conversion: 95% negative by 3 months
  • Persistent positive cultures beyond 3 months suggest drug resistance or non-adherence

Special Considerations:

• Pregnancy: HRZE safe; avoid streptomycin and ethionamide
• HIV co-infection: Same regimens but careful drug interactions with antiretrovirals
• Pediatrics: Similar drugs with weight-based dosing adjustments

Drug-resistant TB represents a significant challenge in TB control, classified based on resistance patterns. Early detection through molecular testing and appropriate treatment regimens are crucial for successful outcomes.

Classification of Drug Resistance:

1. Monodrug Resistance: Resistance to single first-line drug
2. Multidrug-Resistant TB (MDR-TB): Resistance to at least isoniazid and rifampin
3. Extensively Drug-Resistant TB (XDR-TB): MDR-TB + resistance to any fluoroquinolone and ≥1 Group A drug (bedaquiline, linezolid, clofazimine)
4. Pre-XDR TB: MDR-TB + resistance to fluoroquinolone OR Group A drug (but not both)

Risk Factors for Drug Resistance:

• Previous TB treatment
• Contact with known drug-resistant case
• Birth or residence in high drug-resistance prevalence area
• HIV co-infection
• Treatment failure or relapse
• Persistent culture positivity after 2-3 months of treatment

MDR-TB Treatment Approach:

WHO Group Classification (2022 Guidelines):

• Group A (Core drugs): Bedaquiline, Linezolid, Clofazimine
• Group B: Cycloserine/Terizidone, Delamanid/Pretomanid
• Group C: Ethambutol, Pyrazinamide, Imipenem-cilastatin, Amikacin, Streptomycin

Recommended MDR-TB Regimen Structure:

• Minimum 4 drugs likely to be effective
• Include all 3 Group A drugs if possible
• Add Group B drugs to reach 4 drugs
• Supplement with Group C drugs if needed
• Treatment duration: 18-20 months (12-15 months after culture conversion)

Clinical Vignette 2: A 35-year-old man from Bangladesh presents with 3 months of cough, fever, and 15-pound weight loss. He was treated for TB 3 years ago but stopped treatment after 4 months due to side effects. Chest X-ray shows cavitary lesions. GeneXpert MTB/RIF Ultra detects MTB with rifampin resistance.

Discussion: This represents presumptive MDR-TB given previous inadequate treatment and molecular evidence of rifampin resistance. Immediate isolation, complete drug susceptibility testing, and MDR-TB treatment regimen initiation are required. Contact investigation is essential.

Successful TB treatment requires careful monitoring for both treatment response and drug-related adverse effects. Understanding the side effect profile of anti-TB medications enables early recognition and appropriate management.

Common Adverse Effects by Drug:

Isoniazid:

• Hepatotoxicity: Most serious, occurs in 0.1-0.6% of patients
• Peripheral neuropathy: Dose-related, prevented with pyridoxine (B6) 25-50 mg daily
• CNS effects: Seizures (with overdose), psychosis
• Drug interactions: Phenytoin, carbamazepine levels increased

Rifampin:

• Hepatotoxicity: Less common than isoniazid
• Orange discoloration: Urine, tears, sweat (harmless but warn patients)
• Drug interactions: CYP450 inducer - decreases levels of many drugs (warfarin, OCPs, HIV medications)
• Flu-like syndrome: With intermittent dosing
• Thrombocytopenia: Rare but serious

Ethambutol:

• Optic neuritis: Dose-related, usually reversible
• Color vision changes: Red-green discrimination affected first
• Peripheral neuropathy: Less common
• Hyperuricemia: Usually asymptomatic

Pyrazinamide:

• Hepatotoxicity: Dose-related
• Hyperuricemia: Common, may precipitate gout
• Arthralgia: Related to hyperuricemia
• Photosensitivity: Mild

Monitoring Protocol:

Management of Hepatotoxicity:

1. Mild elevation (ALT 2-3× ULN, asymptomatic): Continue treatment with weekly monitoring
2. Moderate elevation (ALT 3-5× ULN or symptoms): Stop hepatotoxic drugs, monitor closely
3. Severe elevation (ALT >5× ULN): Stop all anti-TB drugs, investigate other causes
4. Rechallenge protocol: Sequential reintroduction starting with rifampin, then isoniazid, then pyrazinamide

Special Population Considerations:

• Elderly patients: Increased risk of hepatotoxicity and drug interactions
• Renal impairment: Dose adjustment for ethambutol, streptomycin
• Liver disease: Baseline elevations require careful monitoring
• Pregnancy: Monthly LFT monitoring recommended

TB control requires a comprehensive public health approach combining individual treatment with population-level interventions. Understanding contact investigation, infection control, and prevention strategies is essential for breaking transmission chains.

Contact Investigation: Systematic evaluation of individuals exposed to infectious TB cases is crucial for identifying secondary cases and LTBI. The scope depends on infectiousness of the index case and vulnerability of contacts.

High-Priority Contacts:

• Household members and close social contacts
• Children <5 years old
• Immunocompromised individuals (HIV+, transplant recipients)
• Healthcare workers with occupational exposure
• Individuals exposed in high-risk settings (correctional facilities, homeless shelters)

Contact Investigation Process:

1. Identify and locate contacts within 72 hours of case notification
2. Clinical evaluation with symptom screening, chest imaging, and TST/IGRA
3. Testing timeline: Immediately for symptomatic contacts, 8-10 weeks post-exposure for asymptomatic contacts
4. Treatment decisions based on risk stratification and test results

Infection Control Measures:

Administrative Controls:

• Early identification and isolation of suspected cases
• Prompt diagnostic testing and treatment initiation
• Patient education on cough hygiene
• Healthcare worker TB screening programs

Environmental Controls:

• Negative pressure isolation rooms (≥6 air changes/hour)
• HEPA filtration systems
• Upper room ultraviolet germicidal irradiation

Personal Protective Equipment:

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

Prevention Strategies:

Primary Prevention:

• BCG vaccination in high-burden countries (limited efficacy in adults)
• Addressing social determinants (poverty, malnutrition, overcrowding)
• HIV prevention and treatment

Secondary Prevention:

• LTBI screening and treatment in high-risk populations
• Contact investigation and management
• Regular screening in high-risk settings

Treatment Adherence Support:

• Directly Observed Therapy (DOT): Recommended for MDR-TB, HIV co-infection, and high-risk patients
• Case management: Regular follow-up with TB nurses or healthcare workers
• Incentives and enablers: Transportation vouchers, food assistance, flexible clinic hours
• Treatment supporters: Family members or community health workers

Global TB Control Strategies: The WHO End TB Strategy aims for 90% reduction in TB deaths and 80% reduction in incidence by 2030 through:

1. Integrated, patient-centered care and prevention
2. Bold policies and supportive systems
3. Intensified research and innovation