Classification for TB

Classification System

Many systems have been used to classify people who have TB. The current classification system (Table 1.3) is based on the pathogenesis of TB. Many health departments and private health care providers use this system when describing patients. Thus, it is important for public health workers to be familiar with this system. In particular, public health workers should be aware that any patient with a classification of 3 or 5 should be receiving treatment for TB, and the case or suspected case should be reported.

Class 0

• No exposure to TB; not infected.
• No history of exposure, negative reaction to the tuberculin skin test.

Class 1

• Exposure to TB; No evidence of infection.
• History of exposure, negative reaction to a tuberculin skin test given at least 10 weeks after exposure.

Class 2

• TB Infection; No TB disease.
• Positive reaction to the tuberculin skin test, negative smears and cultures (if done), no clinical or x-ray evidence of TB disease.

Class 3

• Current TB disease.
• Positive culture for M. Tuberculosis (if done), or a positive reaction to the tuberculin skin test and clinical or x-ray evidence of current TB disease.

Class 4

• Previous TB disease (not current).
• Medical history of TB disease, or
• Abnormal but stable x-ray findings for a person who has a positive reaction to the tuberculin skin test, negative smears and cultures (if done), and no clinical or x-ray evidence of current TB disease

Class 5

• TB suspected.
• Signs and symptoms of TB disease, but evaluation not complete.
Source:
Centers for Disease Control
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