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U.S. Department of Health and Human Services

Core Curriculum on Tuberculosis (2000)

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This is an archived document. The links and content are no longer being updated.

Chapter 2 - Transmission and Pathogenesis
Classification System

The current clinical classification system for TB is based on the pathogenesis of the disease (see Table 1). TB disease should be ruled in or out within 3 months. Therefore, a patient should not have a class 5 classification for more than 3 months.

Health care providers should comply with state and local laws and regulations requiring the reporting of TB. All persons with class 3 or class 5 TB should be reported promptly to the state and local health department.

Table 1. Classification System for Tuberculosis

Class	Type	Description
0	No TB exposure Not infected	No history of exposure Negative reaction to tuberculin skin test
1	TB exposure No evidence of infection	History of exposure Negative reaction to tuberculin skin test
2	TB infection No disease	Positive reaction to tuberculin skin test Negative bacteriologic studies (if done) No clinical, bacteriological, or radiographic evidence of active TB
3	TB, clinically active	M. tuberculosis cultured (if done) Clinical, bacteriological, or radiographic evidence of current disease
4	TB Not clinically active	History of episode(s) of TB or Abnormal but stable radiographic findings Positive reaction to the tuberculin skin test Negative bacteriologic studies (if done) and No clinical or radiographic evidence of current disease
5	TB suspected	Diagnosis pending

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Last Reviewed: 05/18/2008
Content Source: Division of Tuberculosis Elimination
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention

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Centers for Disease Control & Prevention
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
Division of Tuberculosis Elimination
Please send comments/suggestions/requests to: CDCINFO@cdc.gov

Core Curriculum on Tuberculosis (2000)

Return to Chapter 2 Main Menu

Chapter 2 - Transmission and Pathogenesis Classification System

Table 1. Classification System for Tuberculosis

Chapter 2 - Transmission and Pathogenesis
Classification System