IEC-CH8: TB infection and TPT

• TB Infection (or previously known as Latent TB infection) is a stage in between uninfected and having active TB. In this stage the person has no symptoms and can only be identified using laboratory tests.

• The vast majority of infected people may never develop TB disease. However, to achieve TB elimination, it is important to treat TB infection in people at risk of developing active TB disease.

• It is a state of persistent immune response to stimulation by Mycobacterium tuberculosis antigens with no evidence of clinically manifested active TB.

• There is no single acceptable/reliable test for direct identification of Mycobacterium tuberculosis infection in humans. Tuberculin Skin Test (TST) and Interferon-gamma release assay (IGRA) are commonly used tests for identifying TB infection.

Resources:

• Latent Tuberculosis Infection Guideline

• Guideline for Programmatic Management of Tuberculosis Preventive Treatment in India

For TB infection, there are two recommended tests which can be used to identify such patients.

Tuberculin Skin Test (TST)

The skin test is done by injecting a small amount (0.5 ml) of TB antigens into the top layer of skin on your inner forearm. If one has ever been exposed to TB bacteria (Mycobacterium tuberculosis), there will be a reaction indicated by the development of a firm red bump (induration) >= 10 mm at the site within 2 days.

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Figure: Tuberculin Skin Test

Interferon-gamma release assay (IGRA)

IGRA is a Blood test. If one has been exposed to TB bacteria, the white blood cell in the blood will release a substance called gamma interferon when the cells are exposed to specific TB antigens.

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Figure: Interferon-gamma release assay (IGRA)

Resources:

• Latent Tuberculosis Infection Guideline
• Guideline for Programmatic Management of Tuberculosis Preventive Treatment in India

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TPT treatment options recommended under NTEP include:

• 3-month weekly Isoniazid and Rifapentine (3HP)
• 6-months daily isoniazid (6H)

Table 1: TPT Options for Target Population; Source: (Guidelines for Programmatic Management of Tuberculosis Preventive Treatment)

Table 2: TPT dosage based on age and weight band recommended by NTEP; Source: Guidelines for Programmatic Management of Tuberculosis Preventive Treatment

Resources

• Guidelines for Programmatic Management of Tuberculosis Preventive Treatment
• National Strategic Plan for TB Elimination

Assessment