What are the diagnostic criteria and treatment options for active Tuberculosis (TB)?

Diagnosis and Management of Active Tuberculosis (TB)

The diagnosis of active TB requires a combination of clinical evaluation, microbiological confirmation through sputum testing (AFB smear, culture, and molecular testing), and radiographic findings, followed by a standard treatment regimen of isoniazid, rifampin, pyrazinamide, and ethambutol for 2 months, then isoniazid and rifampin for 4 months. 1, 2, 3

Diagnostic Criteria for Active TB

Clinical Assessment

• Evaluate for persistent cough (≥2-3 weeks in high TB prevalence areas, ≥3 weeks elsewhere) 1
• Screen for associated symptoms:
  • Fever
  • Night sweats
  • Unexplained weight loss
  • Hemoptysis
  • Fatigue 4, 1
• Assess TB risk factors:
  • Close contact with active TB patients
  • Immigration from TB-endemic countries
  • History of residence in high-risk settings (prisons, homeless shelters, long-term care facilities)
  • HIV infection or immunocompromised status
  • Previous inadequately treated TB 4, 1

Radiographic Evaluation

• Chest radiography is the initial imaging test with high sensitivity for active TB 4

  • Look for characteristic findings:
    • Upper lobe or superior-segment lower lobe infiltrates
    • Cavitary lesions
    • Hilar/mediastinal adenopathy
    • Fibrosis or consolidation 4, 1
  • In immunocompromised patients (especially those with low CD4 counts), chest radiographs may appear deceptively normal 4

• Consider CT for:

  • Patients with equivocal chest radiographic findings
  • Immunocompromised patients with normal chest radiographs but high clinical suspicion
  • High-risk acid-fast bacilli smear-negative patients 4

Microbiological Confirmation

• Collect at least two sputum specimens on different days 1
• Submit specimens for:
  1. Acid-fast bacilli (AFB) smear microscopy
  2. Rapid molecular testing (GeneXpert MTB/RIF)
  3. Liquid culture and drug susceptibility testing (DST) 1
• Nucleic acid amplification test (NAAT) should be performed on the initial respiratory specimen 1

Infection Control

• Patients with suspected TB should be:
  • Provided with and asked to wear a surgical mask
  • Instructed to cover mouth and nose when coughing or sneezing
  • Separated from other patients 4, 1
• Isolation should continue until three consecutive negative sputum smears are obtained and clinical improvement is demonstrated 1

Treatment of Active TB

Standard Regimen for Drug-Susceptible TB

• Initial phase (2 months): Isoniazid, rifampin, pyrazinamide, and ethambutol 2, 3, 5, 6
• Continuation phase (4 months): Isoniazid and rifampin 2, 3, 5, 6
• Ethambutol can be discontinued once susceptibility to isoniazid and rifampin is confirmed 6

Special Populations

HIV Co-infection

• Same regimen as for non-HIV patients, but careful monitoring of clinical and bacteriologic response is essential 6, 7
• If response is slow or suboptimal, therapy should be prolonged on a case-by-case basis 6
• Attention to potential drug interactions between antiretrovirals and TB medications is critical 7

Extrapulmonary TB

• Follow the same principles and drug regimens as for pulmonary TB 6
• Extended treatment duration (9-12 months) for:
  • Miliary TB
  • Bone/joint TB
  • Tuberculous meningitis in children 6

Pregnant Women

• Initial treatment should consist of isoniazid and rifampin 3
• Ethambutol should be included unless primary isoniazid resistance is unlikely (resistance rate <4%) 3
• Streptomycin and routine use of pyrazinamide are not recommended during pregnancy 3

Multi-Drug Resistant TB (MDR-TB)

• Treatment must be individualized based on susceptibility testing 3, 6
• Consultation with a TB expert is recommended 3, 6

Monitoring and Adherence

• Directly Observed Therapy (DOT) is recommended for all patients to ensure compliance 3, 6
• Regular monitoring of treatment response through:
  • Clinical assessment
  • Sputum examinations
  • Radiographic evaluation
  • Monitoring for adverse drug effects 1, 3

Common Pitfalls and Caveats

• Missed diagnosis in immunocompromised patients: TB may present atypically in HIV-infected individuals and other immunocompromised patients 4, 7
• Inadequate isolation: Failure to isolate suspected TB patients can lead to nosocomial transmission 4, 1
• Premature discontinuation of therapy: Incomplete treatment can lead to relapse and drug resistance 3, 8
• Overlooking extrapulmonary TB: TB can affect virtually any organ system, not just the lungs 6
• Failure to perform drug susceptibility testing: All initial isolates should undergo DST to guide appropriate therapy 1

By following this structured approach to diagnosis and management, clinicians can effectively identify and treat active TB, reducing morbidity, mortality, and preventing transmission to others.