Tuberculosis classification

Tuberculosis Microchapters
Home
Patient Information
Overview
Historical Perspective
Classification
Pathophysiology
Causes
Differentiating Tuberculosis from other Diseases
Epidemiology and Demographics
Risk Factors
Screening
Natural History, Complications and Prognosis
Children
HIV Coinfection
Diagnosis
History and Symptoms
Physical Examination
Laboratory Findings
Electrocardiogram
Chest X Ray
CT
MRI
Echocardiography or Ultrasound
Other Imaging Findings
Other Diagnostic Studies
Treatment
Medical Therapy
Special Conditions
Drug-resistant
Surgery
Primary Prevention
Secondary Prevention
Cost-Effectiveness of Therapy
Future or Investigational Therapies
Case Studies
Case #1
Tuberculosis classification On the Web
Most recent articles
Most cited articles
Review articles
CME Programs
Powerpoint slides
Images
American Roentgen Ray Society Images of Tuberculosis classification All Images X-rays Echo & Ultrasound CT Images MRI
Ongoing Trials at Clinical Trials.gov
US National Guidelines Clearinghouse
NICE Guidance
FDA on Tuberculosis classification
CDC on Tuberculosis classification
Tuberculosis classification in the news
Blogs on Tuberculosis classification
Directions to Hospitals Treating Tuberculosis
Risk calculators and risk factors for Tuberculosis classification

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]

Overview

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.

Classification

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

Class	Type of Tuberculosis	Description
0	No TB exposure Not infected	No history of TB exposure A negative TST or IGRA
1	TB exposure No evidence of infection	History of TB exposure A negative TST (given at least 8-10 weeks after exposure) or IGRA
2	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
3	Clinically active TB	Positive culture (if done) for M. tuberculosis Positive 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 TST or IGRA Negative smears and cultures (if done) Absent clinical picture of active TB disease or abnormal x-ray findings
5	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:

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: Applicants with a medical history, physical exam, or CXR findings that indicate pulmonary tuberculosis but: 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.