Prevalence of latent tuberculosis in India, Health News, ET HealthWorld
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Dr Gautam Wankhede
New Delhi: Latent TB is a condition that occurs after an individual is infected by TB bacteria, M. tuberculosis, but does not show symptoms of TB. Unlike patients with active TB, individuals with latent TB do not transmit the disease. In simple terms, people in this situation are infected with TB, but the infection is essentially dormant.
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. According to WHO, approximately one fourth of the worlds population is estimated to be infected with Mycobacterium tuberculosis, and on average, 510 per cent of those who are infected will develop active TB disease over their lifetime. In India, the prevalence rate of latent tuberculosis is very high, around 40 per cent of the population.
The reservoir of latent TB infection (LTBI) is 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. In order to achieve the TB elimination target, testing and treatment of LTBI is essential.
Detection and treatment of latent TB
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, usually due to weak immunity, the person will develop an active infection. Those who have LTBI run a considerably higher risk of developing active TB or having it reactivated than healthy individuals. Thus, people with latent TB infection should be effectively diagnosed and treated to prevent them from developing TB disease.
Several factors can influence the progress from latent TB to active TB disease, such as close contact with people who have active TB, HIV infection, malnutrition, drug use, cancer, diabetes, and weakened immune system. Among people with latent TB infection, HIV infection is the strongest known risk factor for progressing to TB disease. The risk of developing an active TB is around five times higher (~50%) in People Living with HIV (PLHIV). Various studies show that HIV infection increases the risk of TB reactivation from 223% per lifetime to 510% per year.
Until recently, for detecting the latent TB cases, the two most widely used tools 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 results are influenced by an individual's immunity status. Additionally, IGRA is expensive, needs specialized 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. It strikes the right balance. It combines the cost-effectiveness and the ease of the TST with the specificity of the IGRA in the diagnosis of LTBI, and remain unaffected by the BCG vaccination. Further, it is necessary to create new, safer drugs for LTBI treatment.
Also, targeted contact screening programmes among the children and elderly household members of active TB cases, especially in high TB transmission settings, are imperative.
There is a greater need for advanced diagnostics to develop better tests for diagnosing LTBI and forecasting LTBI reactivation.
TB continues to be a significant public health issue in our country, Therefore, the TB programmes should lay emphasis on detection and treatment of LTBI to decrease the likelihood of active TB and to achieve the targets of TB elimination. The management of LTBI should include tracking LTBI cases, efficient diagnostic methods, effective and safe treatment, and monitoring.
Dr Gautam Wankhede, Director of Medical Affairs,
Friday, March 24, 2023 at 6:46 am