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10 facts about Latent TB

In India, the prevalence rate of Latent Tuberculosis infection (LTBI) is very high, with around 40 per cent of the population, with a major barrier to the control and elimination of Tuberculosis. Various studies indicate that a higher prevalence of LTBI would contribute to higher incidence and mortality of TB.

According to WHO, approximately one-fourth of the world’s population is estimated to be infected with Mycobacterium Tuberculosis, and on average, 5-10 per cent of those who are infected will develop active TB disease over their lifetime.

Here are ten facts about Latent TB:

Latent TB is a condition that occurs after an individual is infected by the TB bacteria, M. Tuberculosis but does not show symptoms of TB. TB bacteria is dormant in the body and this phase can last for a very long time – even decades. In the case of active TB cases, TB bacteria reproduces and spreads in the body, causing tissue damage.

Persons with LTBI do not feel sick and do not spread the disease.

Although most of the infected persons do not manifest the disease, they are at high risk of developing active infection and hence represent a reservoir of TB bacteria.

Many individuals with high immunity affected by LTBI, can typically resist the bacteria and prevent them from multiplying. However, if latent TB bacteria become active in the body, the person will develop an active TB infection.

Several factors can influence the progress from latent TB to active TB diseases, such as close contact with people who have active TB, HIV infection, malnutrition, drug use, cancer, diabetes, and a weakened immune system. Among people with latent TB infection, HIV infection is the strongest known risk factor for progressing to TB disease.

The two most widely used tools for detecting latent TB cases are the tuberculin skin test (TST) and interferon-gamma release assays (IGRA). However, TST has poor specificity and low sensitivity as it also shows positive for those who have received the BCG vaccine for TB, while IGRA is expensive, and needs specialised instruments, trained personnel, and labs. Aside from sensitivity issues, neither the IGRA nor the TST can reliably differentiate between active TB disease and LTBI, nor can they predict LTBI reactivation.

The Cy-Tb test is one of the most recent advancements in LTBI diagnosis and is a novel form of the TB skin test.

LTBI can be treated to prevent active TB disease.

TB preventive treatment (TPT) is offered to individuals who are considered to be at risk of developing TB disease. It consists of a course of one or more anti-tuberculosis medicines. TPT is only given to people who are infected with TB bacteria or are at a higher risk of developing TB disease.

The management of LTBI should include tracking of LTBI cases, efficient diagnostic methods, effective and safe treatment, and monitoring.

(Dr Gautam Wankhede is the Director of Medical Affairs of Mylab Discovery Solutions)

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