Classification and Diagnosis of Pulmonary Tuberculosis

Classification System

• The American Thoracic Society and Centers for Disease Control and Prevention have established a standardized classification system for tuberculosis, which includes Class 0: no tuberculosis exposure, not infected, Class 1: tuberculosis exposure, no evidence of infection, Class 2: latent tuberculosis infection, Class 3: clinically active tuberculosis, and Class 4: tuberculosis that is not clinically active 1, 2, 3
• The American Thoracic Society recommends that persons with history of exposure but negative tuberculin skin test be classified as Class 1, and follow-up skin test is recommended 10 weeks after last exposure 1, 2
• The Centers for Disease Control and Prevention suggest that treatment of latent infection may be considered for recent exposures, especially in children <15 years and HIV-infected persons 1
• The American Thoracic Society defines Class 2 as latent tuberculosis infection with positive tuberculin skin test, negative bacteriologic studies, and no clinical/radiographic evidence of active tuberculosis 1, 2
• The Centers for Disease Control and Prevention recommend that chemotherapy status should be documented for Class 2 patients (never received, currently receiving, therapy complete, or therapy incomplete) 1
• The American Thoracic Society defines Class 3 as clinically active tuberculosis with clinical, bacteriological, and/or radiographic evidence of current tuberculosis 1, 3
• The Centers for Disease Control and Prevention state that most definitive establishment of Class 3 is by isolation of M. tuberculosis 1

Diagnostic Criteria for Active PTB

• The American Thoracic Society recommends that active PTB diagnosis be based on clinical presentation, including persistent cough >2-3 weeks with additional symptoms such as fever, night sweats, weight loss, or hemoptysis 4, 5
• The Centers for Disease Control and Prevention suggest that radiographic findings, such as upper-lobe infiltration, cavitation, and pleural effusion, are strongly suggestive of PTB 6
• The American Thoracic Society recommends that bacteriologic confirmation, such as isolation of M. tuberculosis from sputum or other specimens, is essential for active PTB diagnosis 1, 4

Special Considerations

• The Centers for Disease Control and Prevention recommend that HIV status should be known as it may alter the approach to diagnosis and therapy 1, 6

Reporting Requirements

• The American Thoracic Society and Centers for Disease Control and Prevention recommend that all cases of active tuberculosis must be reported to the local health department 1, 3
• The Centers for Disease Control and Prevention state that reporting is essential for public health action, understanding the magnitude and distribution of tuberculosis, accessing health department resources, and epidemiologic evaluation 1, 3

European Classification System

• The European Respiratory Society, WHO, and International Union Against Tuberculosis and Lung Disease define a new case as a patient who has never had drug treatment for TB or who has taken anti-TB drugs for <4 weeks 7
• The European Respiratory Society defines relapse as a patient previously declared cured after one or more full courses of chemotherapy who develops sputum smear-positive or culture-positive disease 7
• The WHO defines treatment failure as a patient who remains or reverts to being smear-positive and/or culture-positive >5 months after commencing treatment 7
• The International Union Against Tuberculosis and Lung Disease defines treatment after interruption as a patient who interrupted treatment for ≥2 months and returned with smear-positive and/or culture-positive sputum 7
• The European Respiratory Society defines chronic case as a patient who remains or becomes smear-positive and/or culture-positive after completing a fully supervised standard retreatment regimen 7