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IM27.{1-4,12} | Tuberculosis Foundations — SDL Guide (Part 3)

Principles of Prevention and Programme Response

The management of tuberculosis at a population level requires the same rigour and precision as management at the individual level. For the foundations SDL, arc step 4 addresses the preventive and programmatic management principles that flow directly from the epidemiology, pathogenesis, and resistance science covered in the preceding blocks. These principles — TB preventive therapy, infection control, contact tracing, and the NTEP operational framework — are the applied translation of foundational science into public health action and are tested directly in clinical practice when managing household contacts, screening high-risk populations, and advising patients on isolation precautions.

TB preventive therapy (TPT): Individuals with latent TB infection (LTBI) at high risk of progression to active disease should receive TPT to prevent that conversion. NTEP-recommended regimens include: (1) 6H — isoniazid 5 mg/kg (maximum 300 mg) daily for 6 months; (2) 3HP — weekly isoniazid + rifapentine for 3 months (preferred where available for better adherence). TPT is mandatory for: all HIV-positive individuals after ruling out active TB; all children aged <5 years who are household contacts of smear-positive cases; patients starting TNF-α blockers or other immunosuppressants after LTBI is confirmed; and other high-risk groups per current NTEP guidelines. Contraindication: active TB must be excluded before TPT — an inadvertent course of isoniazid monotherapy in active TB would amplify resistance.

Infection control principles: In health facilities, TB infection control is a three-tier hierarchy — administrative (separating infectious from non-infectious patients, fast-tracking suspects, reducing patient dwell time), environmental (natural and mechanical ventilation to dilute droplet nuclei concentration — the single most effective physical control measure), and personal protective equipment (N95 respirators for healthcare workers in high-exposure settings — surgical masks are NOT equivalent as they do not filter 1–5 μm particles). In the home, while full respiratory isolation is impractical, key measures include: sleeping separately, opening windows for natural ventilation, and ensuring the patient covers the mouth when coughing. Once on effective treatment, sputum conversion to smear-negative usually occurs within 2 weeks for drug-sensitive TB — after which the patient is essentially non-infectious while completing the regimen.

Contact tracing and screening: All household and close contacts of smear-positive index cases must be screened systematically. The NTEP protocol requires: symptom screening of all contacts; Mantoux/TST testing of children <5 years; HIV testing of contacts with risk factors; clinical evaluation and CXR for symptomatic contacts. Contacts found to have active TB are started on treatment; asymptomatic LTBI contacts in high-risk groups (children <5, HIV-positive) receive TPT regardless of TST result.

NTEP operational framework for treatment: The current NTEP framework mandates: (1) upfront CBNAAT/NAAT testing for ALL presumptive TB cases before treatment; (2) daily FDC-based regimens — the drug-sensitive regimen is 2HRZE/4HRE (intensified in the tb-treatment SDL); (3) Nikshay notification within 24 hours of diagnosis for all patients in public and private sectors; (4) Ni-kshay Poshan Yojana nutritional support automatically triggered on notification; (5) treatment support through trained treatment supporters or video-observed treatment (VOT) where available; (6) treatment outcome monitoring at defined intervals — sputum conversion at 2 months, end-of-treatment.

NTEP Pathway From Presumptive TB to Treatment Outcome

Self-Assessment: Integrating TB Foundations

At this stage you should be able to integrate all five foundational TB competencies into a coherent clinical framework. The following scenarios and reflection prompts are designed to test whether the pieces connect — not just whether each fact was memorised in isolation. TB medicine in India is distinctive in its epidemiological context, the NTEP infrastructure, and the dual-epidemic pressures from HIV and diabetes. A clinician who understands these foundations approaches every patient with cough, weight loss, or unexplained fever through an active TB lens.

Scenario A — Epidemiology applied: A 28-year-old male construction worker from UP presents with 6 weeks of cough and fever. He shares a dormitory with 12 co-workers. His employer has not tested any contacts. How many co-workers are statistically at risk of having been infected if the index patient is smear-positive and symptomatic for 6 weeks?

Analysis: A smear-positive TB patient with active symptoms can infect on average 10–15 contacts per year if in close indoor contact. In a dormitory setting (poor ventilation, prolonged shared air space), the infection probability is higher than the general household attack rate of 5–10%. However, infection rate differs from disease rate — of those infected, only ~10% will develop disease in their lifetime. The programmatic response: all 12 contacts require TST/IGRA testing and clinical screening under NTEP contact-tracing guidelines; contacts aged <5 years and HIV-positive contacts require particular urgency.

Scenario B — Pathogenesis applied to atypical presentation: A 38-year-old woman with HIV (CD4 count 85 cells/μL) is admitted with fever, headache, and confusion. Chest X-ray shows bilateral diffuse small nodular infiltrates. Sputum smear is negative. What form of TB does the radiology suggest, and why is the smear negative despite active disease?

Analysis: Bilateral diffuse 1–2 mm nodules = miliary TB — haematogenous dissemination. In severe HIV immunosuppression (CD4 <200 cells/μL), the granuloma cannot form adequately, so bacilli disseminate without containment. Smear negativity in miliary TB reflects the pattern of disease: bacilli are in the bloodstream and disseminated tissue rather than concentrated in airways — fewer bacilli per millilitre of sputum. This patient requires blood culture for M. tuberculosis, urine AFB culture, and if meningeal signs are present, lumbar puncture for CSF analysis. Management: initiate 4-drug TB regimen and ART within 2–8 weeks (8 weeks if CNS involvement confirmed).

Scenario C — Drug resistance reasoning: A TB patient reports he took "some TB tablets" for 2 months before stopping when he felt better, then resumed treatment 3 months later when symptoms recurred. His current sputum is CBNAAT (Xpert MTB/RIF) positive and shows rifampicin resistance. What is the most likely mechanism of this resistance, and what should NOT be done?

Analysis: This patient has acquired rifampicin resistance from treatment interruption — inadequate treatment duration allowed selection of pre-existing rpoB mutants. He now has RR-TB/MDR-TB. The critical rule: never add a single new drug to this patient's existing regimen (would add one drug to virtual monotherapy, selecting a doubly resistant strain). He requires full DST for second-line drugs, and should be placed on the NTEP MDR-TB regimen under supervision.