Tuberculosis classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]

Overview

Tuberculosis may be classified according to its pathogenesis into 6 categories. This classification divides patients from "class 0", in which the person hasn't had previous exposure to TB, and has a negative TST and IGRA, to "class 5", in which TB is suspected, there are signs and symptoms of the disease, but the evaluation is not complete to confirm the diagnosis. According to the U.S. Citizenship and Immigration Services, immigrants and refugees have a special classification system. This last classifies immigrants and refugees from "no class", in which the person has normal screening tests, to "class B3", in which the person is a recent contact of a known tuberculosis case.

Classification

Below is a table with the current classification system of tuberculosis (TB), based on its pathogenesis:

Class	Type of Tuberculosis	Description
0	No TB exposure Not infected	No history of TB exposure Negative result to a TST or IGRA
1	TB exposure No evidence of infection	History of TB exposure Negative result to a TST (given at least 8-10 weeks after exposure) or IGRA
2	TB infection No TB disease	Positive result to a TST or IGRA Negative smears and cultures (if done) No clinical or x-ray evidence of active TB disease
3	Clinically active TB	Positive culture (if done) for M. tuberculosis Positive result to a TST or IGRA, and clinical, bacteriological, or x-ray evidence of TB disease
4	Previous TB disease (not clinically active)	Medical history of TB disease Abnormal but stable x-ray findings Positive result to a TST or IGRA Negative smears and cultures (if done) No clinical or x-ray evidence of active TB disease
5	Suspected TB	Signs and symptoms of TB disease, but evaluation not complete

CDC TB Classification for Immigrants and Refugees

Tuberculosis classification for immigrants and refugees according to the U.S. Citizenship and Immigration Services, developed by the Centers for Disease Control and Prevention (CDC):

Class	Description
No TB Classification	Applicants with normal tuberculosis screening examinations
Class A TB with waiver	All applicants who have tuberculosis disease and have been granted a waiver
Class B1 TB, Pulmonary	No treatment: Applicants who have medical history, physical exam, or CXR findings suggestive of pulmonary tuberculosis but: Have negative acid-fast bacilli sputum smears Have negative cultures Are not diagnosed with tuberculosis Can wait to have tuberculosis treatment started after immigration Completed treatment: Applicants who were diagnosed with pulmonary tuberculosis and successfully completed directly observed therapy prior to immigration The cover sheet should indicate if the initial sputum smears and cultures were positive and if drug susceptibility testing results are available
Class B1 TB, Extrapulmonary	Applicants with evidence of extrapulmonary tuberculosis The anatomic site of infection should be documented
Class B2 TB, LTBI Evaluation	Applicants who have a tuberculin skin test ≥10 mm or positive IGRA but otherwise have a negative evaluation for tuberculosis The size of the TST reaction or IGRA result, the applicant’s status with respect to latent TB infection (LTBI) treatment, and the medication(s) used should be documented For applicants who had more than one TST or IGRA, all dates and results and whether the applicant’s TST or IGRA converted should be documented Contacts with TST ≥5 mm or positive IGRA should receive this classification (if they are not already Class B1 TB, Pulmonary)
Class B3 TB, Contact Evaluation	Applicants who are a recent contact of a known tuberculosis case The size of the applicant’s TST reaction or IGRA response should be documented Information about the source case, name, alien number, relationship to contact, and type of tuberculosis should also be documented.