Classification of Pulmonary Tuberculosis (PTB) Patients
Pulmonary tuberculosis patients are classified into five categories based on exposure history, infection status, and disease activity: no exposure/not infected (Class 0), tuberculosis exposure without infection (Class 1), latent tuberculosis infection (Class 2), clinically active tuberculosis (Class 3), and tuberculosis that is not clinically active (Class 4). 1
Classification System
The American Thoracic Society and Centers for Disease Control and Prevention have established a standardized classification system for tuberculosis that serves as an operational framework for public health programs:
Class 0: No tuberculosis exposure, not infected - Persons with no history of exposure and a negative tuberculin skin test 1
Class 1: Tuberculosis exposure, no evidence of infection - Persons with history of exposure but negative tuberculin skin test 1
- Follow-up skin test recommended 10 weeks after last exposure
- Treatment of latent infection may be considered for recent exposures, especially in children <15 years and HIV-infected persons 1
Class 2: Latent tuberculosis infection (LTBI), no disease - Persons with positive tuberculin skin test, negative bacteriologic studies, and no clinical/radiographic evidence of active tuberculosis 1
- Chemotherapy status should be documented (never received, currently receiving, therapy complete, or therapy incomplete) 1
Class 3: Tuberculosis, clinically active - Patients with clinically active tuberculosis whose diagnostic procedures are complete 1
- Must have clinical, bacteriological, and/or radiographic evidence of current tuberculosis
- Most definitively established by isolation of M. tuberculosis
- Tuberculin skin test may be positive or negative 1
Class 5: Tuberculosis suspect - Persons whose diagnosis is pending; they should be classified as tuberculosis suspects until diagnostic procedures are complete 1
Diagnostic Criteria for Active PTB
Active PTB (Class 3) diagnosis is based on:
Clinical presentation: Persistent cough >2-3 weeks with additional symptoms such as fever, night sweats, weight loss, or hemoptysis 1
Radiographic findings: Upper-lobe infiltration, cavitation, and pleural effusion are strongly suggestive of PTB 1, 2
Bacteriologic confirmation: Isolation of M. tuberculosis from sputum or other specimens 1
Special Considerations
HIV status should be known as it may alter the approach to diagnosis and therapy 1
Age influences manifestation: Younger patients frequently have constitutional symptoms and hemoptysis, while older patients often present with respiratory symptoms and pleural effusion 3
Comorbidities affect presentation: Diabetic patients are more likely to present with cavitary nodules 3
Post-tuberculosis lung damage (PTLD) is a common consequence of PTB that can lead to persistent symptoms and disability 4
Reporting Requirements
By law, all cases of active tuberculosis must be reported to the local health department 1
Reporting is essential for:
- Public health action at local, state, and national levels
- Understanding the magnitude and distribution of tuberculosis
- Accessing health department resources for proper case management
- Epidemiologic evaluation, including identification of source cases and contacts 1
All positive smear, culture, susceptibility, and nucleic acid amplification results should be reported to health departments and treating physicians within one working day 1
European Classification System
The European Respiratory Society, WHO, and International Union Against Tuberculosis and Lung Disease use similar but slightly different definitions:
New case: Patient who has never had drug treatment for TB or who has taken anti-TB drugs for <4 weeks 1
Relapse: Patient previously declared cured after one or more full courses of chemotherapy who develops sputum smear-positive or culture-positive disease 1
Treatment failure: Patient who remains or reverts to being smear-positive and/or culture-positive >5 months after commencing treatment 1
Treatment after interruption: Patient who interrupted treatment for ≥2 months and returned with smear-positive and/or culture-positive sputum 1
Chronic case: Patient who remains or becomes smear-positive and/or culture-positive after completing a fully supervised standard retreatment regimen 1
Understanding and applying this classification system is crucial for appropriate patient management, public health surveillance, and tuberculosis control efforts.