Tuberculosis classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mashal Awais, M.D.[2]; João André Alves Silva, M.D. [3]


Tuberculosis can be classified into 6 main categories according to exposure, symptoms, and diagnostic testing. The classification ranges from Class 0, in people with no previous exposure to TB and negative tuberculin skin testing and/or interferon-gamma release assay (2 methods of screening for TB), to Class 3 for active TB infection and Class 5 for suspected TB infection based on signs and symptoms of the disease. The U.S. Citizenship and Immigration Services has also designed a special classification for immigrants and refugees according to the risk of infection.


Below is a table of the current classification system of tuberculosis (TB), according to its pathogenesis:[1]

Class Type of Tuberculosis Description


No TB exposure
Not infected

No history of TB exposure
A negative TST or IGRA


TB exposure
No evidence of infection

History of TB exposure
A negative TST (given at least 8-10 weeks after exposure) or IGRA


TB infection
No TB disease

Positive TST or IGRA
Negative smears and cultures (if done)
Absent clinical picture of active TB disease or abnormal x-ray findings


Clinically active TB

Positive culture (if done) for M. tuberculosis
Positive TST or IGRA, and clinical, bacteriological, or x-ray evidence of TB disease


Previous TB disease (not clinically active)

Medical history of TB disease
Abnormal but stable x-ray findings
Positive TST or IGRA
Negative smears and cultures (if done)
Absent clinical picture of active TB disease or abnormal x-ray findings


Suspected TB

Clinical manifestations of TB disease, but incomplete evaluation. The diagnosis s pending. The patient should not be in this class for more than three months.

CDC TB Classification for Immigrants and Refugees

Based on the U.S. Citizenship and Immigration Services, developed by the Centers for Disease Control and Prevention (CDC), tuberculosis for immigrants and refugees s classified into the following categories: [2]

Class Description Travel Clearance

No TB Classification

Applicants with normal tuberculosis screening examinations. No discernible HIV infection and normal CXR.

Valid for 6 months from evaluation

Class A TB

All applicants who have tuberculosis disease including applicants with extrapulmonary TB. In addition, CXR indicates pulmonary TB disease, regardless of sputum smear and culture results.

Not cleared for travel until treatment is completed. Exceptions are available for granted waivers.
Class B0 TB, Pulmonary Applicants who were previously diagnosed with TB or came to the physician during the TB treatment course. Additionally, successful completion of the Division of Global Migration and Quarantine (DGMQ) prior to immigration is required. It can be valid for 3 months from the last negative culture results.

Class B1 TB, Pulmonary

No treatment:

  • Have negative acid-fast bacilli sputum smears
  • Have negative cultures
  • Are not diagnosed with tuberculosis
  • They can initiate tuberculosis treatment after immigration

Completed treatment:

  • Applicants who had a previous diagnosis of pulmonary tuberculosis and successfully completed directly observed therapy prior to immigration
  • The cover sheet must include whether the initial sputum smears and cultures were positive and if drug susceptibility testing results are available
It can be valid for 3 months from the last negative culture results.

Class B1 TB, Extrapulmonary

Applicants with evidence of extrapulmonary tuberculosis, with normal CXR and negative sputum smears and cultures.
The anatomic site of infection should be documented

It can be Valid for 3 months from the last negative culture results.

Class B2 TB, LTBI Evaluation

Applicants who have a TST ≥10 mm or positive IGRA but otherwise tuberculosis evaluation is negative
The TST reaction size or IGRA result, the applicant’s status regarding latent TB infection (LTBI) treatment, and the medication(s) used must be included
Applicants with more than one TST or IGRA, all results and dates must be ncluded
Contacts with TST ≥5 mm or positive IGRA should be classified according to this classification (if they are not already Class B1 TB, Pulmonary)

Valid for 6 months from completion of evaluation.

Class B3 TB, Contact Evaluation

Applicants who have been in contact of a known tuberculosis case
The size of the applicant’s TST reaction or IGRA result must be included
The name, source case, alien number, relationship to contact, and type of tuberculosis must be included.

Valid for 6 months from completion of the evaluation.

Risk Classification Necessity of testing Frequency of testing
Low Risk Settings where Tb infected individuals are unlikely to be present Not required unless there has been exposure to TB
Medium Risk Settings where health care workers (HCWs) are likely to encounter individuals with TB Testing should be repeated every year
Potential Ongoing Transmission Settings wehere person to person transmission of TB was documented in the past year Testing should be repeated every 8 weeks until making sure that there has been no ongoing transmission.


  1. "TB Classification".
  2. "TB Classification US Citizenship and Immigration Services" (PDF).

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