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U.S. Department of Health and Human Services

  

Core Curriculum on Tuberculosis, 2000

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

 


Released October 2008
Centers for Disease Control and Prevention
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
Division of Tuberculosis Elimination - http://www.cdc.gov/tb

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