Context:
India’s fight against tuberculosis (TB) is hindered by subclinical TB, where individuals have the disease without typical symptoms. National surveys reveal that over 40% of TB cases are subclinical, complicating detection and treatment efforts. Despite progress in reducing TB mortality, the slow decline in incidence is linked to the under-detection of subclinical cases, necessitating innovative approaches and sustained public health interventions.
The Prevalence of Subclinical TB
Survey Findings:
- The national TB prevalence survey (2019-2021) revealed that 42.6% of TB cases detected were subclinical, meaning these cases would have been missed without the inclusion of a chest X-ray in the screening process. Similarly, a TB prevalence survey in Tamil Nadu found 39% of cases to be subclinical.
- Subclinical TB is not limited to India; prevalence surveys in high-burden countries across Asia and Africa have found significant proportions of subclinical TB, with the median prevalence being around 50%. Depending on the definition used, this figure can range from 30% to as high as 80%.
Impact on TB Incidence
- The presence of subclinical TB is likely a major reason why the incidence of TB has been decreasing so slowly, despite improvements in detecting and treating symptomatic cases. While the focus on symptomatic TB has helped reduce mortality, it has not had the same impact on incidence rates, which are only declining by 2-3% per year globally—far short of what is needed to achieve TB elimination goals.
Challenges in Addressing Subclinical TB
Screening and Detection:
- Detecting subclinical TB requires a different approach from traditional TB screening, which focuses on symptomatic individuals. Countries like Vietnam have demonstrated the effectiveness of symptom-agnostic screening, where entire populations are screened regardless of symptoms. Such screening has shown a significant reduction in TB prevalence when conducted consistently over several years.
- Implementing large-scale screening for subclinical TB in India would require innovative strategies, such as mobile units equipped with handheld X-ray machines to conduct regular camps in high-burden areas. However, this approach poses significant logistical challenges, especially in convincing seemingly healthy individuals to undergo screening.
Treatment Adherence:
- Convincing individuals with subclinical TB to begin and complete treatment is another challenge. These individuals often do not feel ill and may not see the need for a lengthy treatment regimen. Studies have shown that people with fewer symptoms tend to have better treatment outcomes but are also more likely to drop out of treatment.
- Addressing this issue will require extensive counselling, education, and follow-up to ensure that individuals understand the importance of completing their treatment, both for their health and for public health.
Public Health Implications
High-Risk Populations
- While subclinical TB has been found in the general population, certain high-risk groups, such as those living in densely populated areas or tribal communities, may require targeted screening efforts. For example, the Piramal Foundation’s program that screened 10 million people in tribal areas found 10,000 TB patients, highlighting the potential impact of focused interventions.
- Regular screening in high-burden areas, such as Northern states and cities like Mumbai, could significantly reduce TB prevalence, but this would need to be a sustained effort rather than a one-time initiative.
Transmission Risk:
- People with subclinical TB may still be infectious, even without a cough. Some prevalence surveys have found that individuals with subclinical TB had smear-positive disease, indicating a high bacillary burden. This means they could still be transmitting the infection through breathing, talking, or other activities, contributing to the continued spread of TB in the community.
- Understanding the dynamics of subclinical TB, including the risk factors for progression to active TB or self-cure, is crucial for developing effective public health strategies.
AI-Based Screening
The Central TB Division in India is exploring the use of AI-based chest X-rays for TB screening. Several companies have applied to the Indian Council of Medical Research (ICMR) for validation of their AI algorithms, and two companies have already been approved. This technology could potentially enhance the detection of subclinical TB by automating and standardizing the screening process.
Way Forward:
- Community Awareness Campaigns: Intensify public education on the risks of subclinical TB to encourage participation in screening programs.
- Targeted High-Risk Screening: Focus screening efforts on high-risk populations and densely populated urban areas using mobile units and AI-based tools.
- Strengthen Primary Healthcare: Equip local healthcare centers with better diagnostic tools and trained staff for early detection and treatment adherence support.
- Government Initiatives: Expand the National Tuberculosis Elimination Programme (NTEP) to include systematic screening for subclinical TB, incorporating AI-based chest X-rays and mobile diagnostic units in remote areas.
- Research and Data Collection: Invest in research to understand the progression of subclinical TB and refine strategies to prevent its spread.
- Public-Private Partnerships: Collaborate with private sectors and NGOs to expand screening and treatment efforts in underserved areas.
Subclinical TB presents a significant challenge in India’s fight against tuberculosis. While the focus on symptomatic cases has led to improvements in TB mortality, the high prevalence of subclinical TB may be hindering progress in reducing the overall incidence of the disease. Addressing this issue will require innovative screening strategies, improved treatment adherence, and a better understanding of the transmission risks associated with subclinical TB. With continued efforts and the integration of new technologies, India can make strides towards its goal of TB elimination.