World Health Organization

TB Case Definitions

Module 4 – March 2010

Project Partners

Funded by the Health Resources and Services Administration (HRSA)

Module Overview

TB Case Definitions Categories for

Classifying TB Cases• Site of Disease

• Bacteriologic Result

• HIV Status

• History of Prior Treatment

TB Case Registration Groups

Learning Objectives

Objectives: At the end of this presentation,participants will be able to:

Define TB cases utilizing the World Health Organization case definitions for tuberculosis

State the four key features important to classifying TB cases

Categorize TB cases utilizing the World Health Organization registration groupings

TB Case Definitions

Why do we define and categorize TB cases?

Purpose of TB Case Definitions

Correct categorization of patients before starting treatment for TB is essential:• for proper patient registration and case notification

• to select the appropriate treatment regimen

• to standardize the process of data collection for TB control

• to evaluate the proportion of cases according to site, bacteriology, and treatment history

• for cohort analysis of treatment outcomes

• to accurately monitor trends and evaluate the effectiveness of TB programs

TB Case Definitions

Tuberculosis suspect — Any person who presents with symptoms or signs suggestive of TB (e.g., a cough of long duration, > 2 weeks)

Case of tuberculosis• a definite case of TB (defined next slide) or • diagnosed by a health worker with the plan to treat

with a full course of anti-TB treatment

Any person started on TB treatment should be recorded as a case. Incomplete “trial” TB treatment should not be given as a method for diagnosis

TB Case Definitions (2)

Definite case of tuberculosis: A patient with M. tuberculosis complex identified from a clinical specimen by culture or newer method (e.g., nucleic acid amplification, molecular beacon or line probe assays)

In countries where M. tuberculosis cannot routinely be identified, a pulmonary case with one or more initial sputum smears positive for acid-fast bacilli (AFB) is also considered a “definite” case

Categories for Classifying TB Cases

TB Case Classifications

TB cases are also classified according to:

1. Anatomical site of TB disease

2. Bacteriologic results (including drug resistance)

3. History of previous TB treatment

4. HIV status of the patient

Anatomical Site of Disease

Pulmonary Tuberculosis (PTB): Refers to disease involving the lung parenchyma• A patient with both pulmonary and extra-

pulmonary TB constitutes a case of PTB

• Miliary TB is classified as PTB because there are lesions in the lungs

Anatomical Site of Disease (2)

Extra-pulmonary Tuberculosis (EPTB): Refers to TB disease of organs other than the lungs. Therefore the following constitute a case of EPTB:• Tuberculous intrathoracic lymphadenopathy

(mediastinal and/or hilar)

• Tuberculous pleural effusion, without radiographic abnormalities in the lungs

• Extrathoracic TB

Anatomical Site of Disease (3) Diagnosis of EPTB should be based on a

decision to treat with a full course along with:• One culture-positive specimen; or• Histological specimen; or• Strong clinical evidence consistent with active

EPTB and a decision to treat with a full course of anti-TB treatment

Where several EPTB sites are involved, the case definition depends on the site representing the most severe form of disease

Classify as PTB if both pulmonary and extra-pulmonary sites involved

Bacteriologic Result

Includes smear, culture and newer methods for identification of M. tuberculosis

Defining the AFB smear result is important :• to identify smear-positive cases = most

infectious; most likely to transmit TB to others

• to identify sputum smear-negative cases, especially HIV positive persons

• to record, report, and evaluate program performance

Bacteriologic monitoring for treatment response is most practical in smear-positive patients

Bacteriologic Result (2)

Pulmonary TB: Sputum smear-positive

Where there is a functional EQA system:• A patient with one or more sputum

specimens that are AFB smear-positive is considered a PTB case

Bacteriologic Result (2)

Pulmonary TB: Sputum smear-positive

Where there is not yet a functional EQA system, then one of the following apply at treatment start:• > 2 sputum specimens are AFB smear-positive; or

• at least 1 sputum specimen is AFB smear-positive and radiographic abnormalities consistent with active PTB are present and determined by a clinician; or

• at least one sputum specimen is AFB smear-positive plus culture is positive for M. tb

Bacteriologic Result (3)

Pulmonary TB: Sputum smear-negative

At least 2 sputum specimens are negative for AFB at start of treatment

No specimen is smear positive

Obtain TB culture for all smear-negative cases

Bacteriologic Result (4)

Pulmonary TB: Sputum smear-negative

Defined as:

1. Smear-negative but culture-positive for M.tb; or

2. Meet the following criteria:• decision by a clinician to treat with a full course of

anti-tuberculosis chemotherapy, and

• radiographic abnormalities consistent with active PTB, and either: laboratory or strong clinical evidence of HIV infectionor no response to a course of broad-spectrum non-TB

antibiotics (if HIV-negative or status unknown)

Bacteriologic Result (5)

Pulmonary TB: Smear not done

PTB cases without smear results are no longer classified as smear-negative!

Classify as “smear not done” on the TB Register and annual survey

ISTC Standard 3: Extrapulmonary Specimens

For all patients suspected of having extrapulmonary TB, appropriate specimens from the suspected sites of involvement should be obtained for microscopy, culture and histopathological examination.

Bacteriologic Result (6)

International Standards for Tuberculosis Care, 2009

HIV Status

Determining and recording HIV status for TB cases is critical for:• Making treatment decisions• Monitoring trends• Assessing program performance

The 2006 updated TB Register and TB Treatment Card include dates for:• HIV testing• Co-trimoxazole initiation• ART initiation

History of Previous TB Treatment

A case should be defined according to whether or not the patient has previously received TB treatment in order to:

• Identify patients at increased risk of acquired drug resistance

• Provide epidemiological monitoring of the TB epidemic and program performance at regional and country levels

TB Case Registration Groups

TB Case Registration Groups

New case: A patient who has never had treatment for TB or who has taken anti-tuberculosis drugs for less than 1 month

Previously Treated case: A patient who has received a month or more of anti-TB drugs in the past (with positive or negative bacteriology)• Case is further classified by outcome of most

recent course of treatment

No “chronic” category

TB Case Registration Groups (2)

Relapse: A patient previously treated for TB who has been declared cured or treatment completed, and is diagnosed with bacteriologically positive TB (smear, culture or newer means of identifying M.tb)

Treatment after Failure: A patient who is started on a re-treatment regimen after having failed previous treatment

Treatment after Default: A patient who returns to treatment following interruption of treatment for > 1 month and is positive bacteriologically

Previously treated cases

TB Case Registration Groups (3)

Transfer in: A patient who has transferred from another TB register to continue treatment

Other: All cases that do not fit the previous definitions. This includes:• Previous treatment history is unknown• Previously treated, but outcome is unknown• Returned to treatment with:

• smear-negative PTB• bacteriologically negative EPTB

TB Case Registration

Activity

Summary

Every TB patient should be assessed for the four key features of case definition so they can be classified correctly and begin treatment

Every TB patient should have TB case registration group determined prior to initiation of TB treatment