Operational Handbooks

2.6 Tests for TB infection

TB infection is a state of persistent immune response to Mtb antigens with no evidence of clinically manifest TB disease (35). People with TB infection have no signs or symptoms of TB disease, are not infectious, have normal or stable images on chest X-ray (CXR), and have negative microbiological tests (if such tests are performed). It is estimated that about 25% of the world’s population has been infected with Mtb (1), of whom 5–10% will develop TB disease over their lifetime (36).

Annex 4. Skin tests for tuberculosis infection – detailed description

This annex provides step-by-step procedures for administering and reading two types of skin test for tuberculosis (TB) infection: the tuberculin skin test (TST) and Mycobacterium tuberculosis antigen-based skin tests (TBSTs). The photographs used in this annex were kindly provided by Dr Richard Menzies and colleagues.

A1 – Test administration

Step 1. TB Screening check

Annex 3. Implementation of next-generation sequencing technologies

The World Health Organization (WHO) recently published The use of next-generation sequencing for the surveillance of drug-resistant tuberculosis: an implementation manual (1) which provides practical guidance on planning and implementing next-generation sequencing (NGS) technology for characterization of Mycobacterium tuberculosis complex (MTBC) bacteria. In this manual, the focus is on the detection of mutations associated with drug resistance for the surveillance of drug resistance in tuberculosis (TB).

Annex 2. Drug susceptibility testing methods and critical concentrations

Culture-based DST methods for certain anti-tuberculosis (anti-TB) medicines are reliable and reproducible, but these methods are time consuming, and require specific laboratory infrastructure, skilled staff and adherence to quality control. The WHO Technical manual for drug susceptibility testing of medicines used in the treatment of tuberculosis (1) describes the methods, media, sources of drug powders and critical concentrations for conducting drug susceptibility testing (DST) of Mycobacterium tuberculosis complex (MTBC isolates).

6.8 Illustrative algorithm combinations

To aid understanding of how the different algorithms interlink to provide a final diagnosis for a person, illustrative scenarios are presented in Fig. 6.8, Fig. 6.9 and Fig. 6.10. Three scenarios are provided, with two simulated pathways in each. The scenarios are based on three epidemiological settings: high TB/HIV, high Hr-TB and high MDR/RR-TB. These examples are for illustrative purposes only – they do not represent a specific recommendation.

6.7 Algorithm 4 – Testing for TB infection

An integrated algorithm for TPT among contacts (aged <5 years), people living with HIV and other risk groups has been released by WHO as Module 1 of the guidelines (17). For household contacts who are aged 5 years and older and who are not HIV-positive, testing for TB infection is advised as part of their care. Given that contacts are also at risk of TB disease, an integration of testing for TB infection with TB screening would be an important step to enhance implementation.