Tuberculosis — Epidemiology & Control

Tuberculosis remains India's single largest infectious-disease killer and the highest-yield Community Medicine topic for NEET PG. This note builds the public-health scaffold: how TB burden is measured, how the National TB Elimination Programme (NTEP, formerly RNTCP) defines and treats cases, the DOTS philosophy, drug-resistant TB, newer diagnostics, and the elimination targets. Master the numbers — examiners love cut-offs, regimens, and case definitions.

1. Magnitude & epidemiological measures

TB is caused by Mycobacterium tuberculosis (and rarely M. bovis), an acid-fast bacillus with a slow generation time (~16–20 hours) and a predilection for the lung apex (high oxygen tension). India carries the world's largest TB burden — roughly 26–28% of global incident cases.

Key epidemiological indices you must distinguish:

Index	What it measures	Notes
Incidence	New + relapse cases per 1,00,000/year	India ~195/lakh (declining)
Prevalence	All existing cases at a point in time	National TB Prevalence Survey 2019–21
ARTI	Annual Risk of Tuberculous Infection	Best single index of TB transmission in a community
Case fatality ratio	Deaths among cases	Untreated smear-positive ~50–65% over 5 yrs
Infection prevalence	% tuberculin-positive	Tracks cumulative exposure

High-yield: The Annual Risk of Tuberculous Infection (ARTI) is the single best epidemiological index to monitor the trend of TB in a community, because it reflects ongoing transmission and is independent of BCG and case-detection efforts.

ARTI calculation

ARTI is derived from the prevalence of infection (P) in unvaccinated children using the formula:

ARTI ≈ 1 − (1 − P)^(1/a), where a = average age of the surveyed children.

A rule of thumb taught for exams: a 1% ARTI corresponds to roughly 50 new smear-positive (infectious) cases per 1,00,000 population per year. A falling ARTI signals effective control. The tuberculin survey in unvaccinated children is the classic method to estimate it.

High-yield: A decline in ARTI of about 10% per year reflects good programme performance and is the kind of target historically used to gauge transmission interruption.

2. Diagnosis & investigation of choice

The diagnostic algorithm has shifted decisively toward molecular testing.

Stepwise approach (presumptive pulmonary TB):

1. Identify presumptive TB → cough ≥ 2 weeks, fever, weight loss, haemoptysis, night sweats; any contact of a TB patient; PLHIV with any TB symptom.
2. Upfront molecular test (NAAT) → CBNAAT (GeneXpert MTB/RIF) or Truenat is now the recommended first-line investigation. It detects M. tuberculosis DNA and rifampicin resistance simultaneously in ~2 hours.
3. Sputum smear microscopy (ZN / fluorescent LED) → still used where NAAT unavailable; detects ~10,000 bacilli/mL.
4. Culture (LJ medium / liquid MGIT) → gold standard for confirmation and drug-susceptibility testing (DST). LJ takes 6–8 weeks; liquid culture ~2 weeks.
5. Chest X-ray → sensitive but not specific; used for screening and pulmonary assessment.
6. Drug-susceptibility testing (DST) → Line Probe Assay (LPA) for first- and second-line drugs; liquid culture DST.

High-yield: CBNAAT / Truenat is the recommended upfront diagnostic test under NTEP. Its dual advantage is rapid detection of TB and rifampicin resistance — making it pivotal for detecting MDR-TB early.

Test	Detects	Turnaround	Sensitivity note
ZN smear	AFB	Same day	Needs ~10⁴ bacilli/mL
Fluorescent LED microscopy	AFB	Same day	More sensitive than ZN
CBNAAT (GeneXpert)	MTB DNA + RIF resistance	~2 hrs	Detects ~130 bacilli/mL
Truenat	MTB + RIF resistance	~1 hr	Chip-based, portable
Culture (LJ/MGIT)	Viable bacilli	2–8 wks	Gold standard, enables DST
LPA	First/second-line resistance	1–2 days	For DST

3. NTEP / RNTCP — programme essentials

The Revised National TB Control Programme (RNTCP, 1997) was renamed the National TB Elimination Programme (NTEP) in 2020, reflecting the elimination ambition. It operates under the National Health Mission and adopts the WHO-recommended DOTS strategy and its successor, the End TB Strategy.

DOTS — five components (mnemonic: "Political-Diagnosis-Drugs-DOT-Reporting")

1. Political and administrative commitment with sustained funding.
2. Diagnosis by quality-assured bacteriology (now molecular).
3. Uninterrupted supply of quality drugs.
4. Directly Observed Treatment (DOT) — a treatment supporter watches the patient swallow each dose.
5. Systematic monitoring, recording and reporting (now via Nikshay).

High-yield: DOTS stands for Directly Observed Treatment, Short-course. The "directly observed" element addresses non-adherence — the chief driver of treatment failure and acquired drug resistance.

Daily fixed-dose combination (FDC) regimen

India transitioned from intermittent (thrice-weekly) to a daily weight-band FDC regimen delivered as blister packs. Drugs: H (isoniazid), R (rifampicin), Z (pyrazinamide), E (ethambutol).

Patient type	Intensive phase	Continuation phase
New (drug-sensitive)	2 months HRZE	4 months HRE
Previously treated (DS, modern guidance)	Based on DST; regimen individualised	—
Paediatric (DS)	2 months HRZE (weight band)	4 months HRE

High-yield: Under current NTEP guidance, the Category II regimen (with streptomycin / extended retreatment) has been discontinued. All previously treated patients undergo DST and are managed accordingly; the historical "Cat I = new, Cat II = retreatment with S" framework is now outdated — but examiners may still test the old scheme, so know both.

Streptomycin is no longer part of the standard first-line FDC. Note pyridoxine (vitamin B6) is co-prescribed with isoniazid to prevent peripheral neuropathy.

4. NTEP case definitions

Precise definitions are heavily tested.

• Presumptive TB: any person with symptoms/signs suggestive of TB (cough ≥ 2 weeks, fever, weight loss, etc.).
• Microbiologically confirmed TB: biological specimen positive by smear, culture, or NAAT (CBNAAT/Truenat).
• Clinically diagnosed TB: not microbiologically confirmed but diagnosed by a clinician and decided for full treatment.
• New case: never had ATT or took anti-TB drugs for < 1 month.
• Previously treated case: received ≥ 1 month of anti-TB drugs in the past. Subtypes:
  • Relapse — previously declared cured/treatment-completed, now again diagnosed.
  • Treatment after failure — previous treatment failed.
  • Treatment after lost to follow-up (LTFU) — returned after interrupting ≥ 1 month (the old "default").
• Treatment outcomes: Cured, Treatment completed, Treatment failed, Died, Lost to follow-up, Not evaluated, Treatment success (= cured + completed).

High-yield: "Lost to follow-up" replaces the older term "default" and is defined as a patient whose treatment was interrupted for ≥ 1 consecutive month. "Treatment failure" was historically smear-positive at ≥ 5 months; under molecular monitoring it is increasingly based on persistent positivity or emergence of resistance.

5. Drug-resistant TB (DR-TB)

Resistance type	Definition
Mono-resistance	Resistance to one first-line drug
Poly-resistance	Resistance to ≥ 2 first-line drugs, but not both H + R
MDR-TB	Resistance to at least isoniazid AND rifampicin
Pre-XDR-TB	MDR/RR-TB + resistance to any fluoroquinolone
XDR-TB	MDR + fluoroquinolone + a Group A drug (bedaquiline/linezolid) — per updated WHO definition
RR-TB	Rifampicin resistance (treated like MDR)

High-yield: MDR-TB = resistance to at least isoniazid + rifampicin (the two most potent first-line drugs). Rifampicin resistance detected on CBNAAT is the trigger to start an MDR work-up and refer for the longer/shorter DR-TB regimen.

DR-TB management uses newer oral regimens centred on bedaquiline, linezolid, levofloxacin/moxifloxacin, clofazimine, cycloserine, etc. NTEP has adopted shorter all-oral bedaquiline-containing regimens (e.g., BPaLM — bedaquiline, pretomanid, linezolid, moxifloxacin) for eligible MDR/RR-TB, replacing injectable-based regimens.

6. Nikshay & notification

Nikshay is the web-based, real-time case-based surveillance and patient-management portal of NTEP.

Functions to remember:

• Notification of every diagnosed TB case (mandatory for all providers — public and private).
• Patient registration, treatment monitoring, contact tracing, drug-resistance tracking.
• Direct Benefit Transfer (DBT) — including the nutritional support scheme.
• Nikshay Poshan Yojana: ₹500/month (revised upward in recent years) to every notified TB patient for nutritional support, paid via DBT.
• Nikshay Mitra (Ni-kshay Mitra): community/donor adoption of TB patients for nutritional and other support under the Pradhan Mantri TB Mukt Bharat Abhiyan (2022).

High-yield: TB is a notifiable disease in India (Gazette notification 2012, reinforced 2018). Every health-care provider — including private practitioners, labs, and chemists dispensing anti-TB drugs — must notify each case to the government via Nikshay. Failure is punishable under the Epidemic Diseases Act / IPC provisions.

7. Prevention & control

• BCG vaccination: live attenuated M. bovis; given at birth (0.05 mL intradermal, left upper arm) under the Universal Immunization Programme. Protects best against severe childhood forms — miliary TB and TB meningitis; protection against adult pulmonary TB is variable.
• TB Preventive Treatment (TPT): for household contacts, PLHIV, and other high-risk groups. Regimens include 6 months isoniazid (6H), 3HP (weekly isoniazid + rifapentine ×3 months), or 3HR.
• Airborne infection control: ventilation, UV germicidal irradiation, respiratory hygiene, N95 for staff.
• Active case finding (ACF) among vulnerable populations.
• Contact tracing of all index-case household contacts.

High-yield: BCG's most reliable protection is against tuberculous meningitis and miliary (disseminated) TB in children — this is the classic single-best-answer.

8. India's elimination targets

High-yield: India set the goal of TB elimination by 2025, five years ahead of the global SDG target of 2030 under WHO's End TB Strategy. "Elimination" here is defined operationally as reducing incidence to < 1 case per 1,00,000 population.

WHO End TB Strategy milestones (baseline 2015): 90% reduction in TB deaths and 80% reduction in incidence by 2030, and 95%/90% by 2035, with zero catastrophic costs for affected families. The flagship Indian campaign is the Pradhan Mantri TB Mukt Bharat Abhiyan and the National Strategic Plan.

9. Complications & associations

• Pulmonary: haemoptysis, massive haemoptysis (Rasmussen aneurysm), bronchiectasis, fibrosis, aspergilloma in old cavities, cor pulmonale.
• Extrapulmonary: TB meningitis, Pott's spine, renal/genitourinary TB, lymphadenitis (scrofula), pericardial effusion, intestinal/peritoneal TB.
• Programmatic complications: drug toxicity — isoniazid → hepatotoxicity + peripheral neuropathy; rifampicin → hepatotoxicity, orange secretions, enzyme induction; pyrazinamide → hyperuricaemia/hepatotoxicity; ethambutol → retrobulbar optic neuritis; streptomycin → ototoxicity + nephrotoxicity.
• TB-HIV syndemic: HIV is the strongest risk factor for progression from latent to active TB; IRIS may occur after starting ART.

10. Key differentials

• Pulmonary TB vs lung carcinoma, community-acquired pneumonia, lung abscess, sarcoidosis, fungal infection (histoplasmosis), non-tuberculous mycobacteria (NTM).
• TB lymphadenitis vs lymphoma, metastatic node, sarcoid, reactive lymphadenopathy.
• TB meningitis vs partially treated bacterial meningitis, fungal (cryptococcal) meningitis, viral meningitis — CSF shows lymphocytic pleocytosis, high protein, low glucose.

Recently asked / exam angle

• CBNAAT interpretation: a question may give "MTB detected, Rifampicin resistance detected" → answer: refer for DR-TB regimen / start MDR work-up.
• NSP / smear grading: scanty, 1+, 2+, 3+ grading and what constitutes a positive result; conversion at end of intensive phase.
• ARTI calculation and its meaning as the best index of transmission.
• MDR-TB definition (H + R) — a perennial single-best-answer.
• Nikshay functions and mandatory notification by private practitioners.
• Nikshay Poshan Yojana amount and DBT.
• BCG protection against miliary TB and TB meningitis; site and dose.
• Daily FDC regimen 2HRZE/4HRE and discontinuation of Category II.
• India's 2025 elimination target vs global 2030 SDG target.
• Pyridoxine co-administration with INH; ethambutol → optic neuritis as the classic drug-toxicity match.
• End TB Strategy milestones (90% mortality / 80% incidence reduction by 2030).
• RNTCP → NTEP rename (2020) and DOTS five components.

Rapid revision

1. ARTI is the best single index of TB transmission in a community; ~1% ARTI ≈ 50 new infectious cases/lakh/year.
2. CBNAAT/Truenat is the upfront diagnostic — detects MTB and rifampicin resistance in ~2 hours.
3. Culture (LJ/MGIT) remains the gold standard and enables DST.
4. MDR-TB = resistance to isoniazid + rifampicin, at minimum.
5. XDR-TB (updated) = MDR + a fluoroquinolone + a Group A drug (bedaquiline/linezolid).
6. New DS-TB regimen = 2HRZE / 4HRE daily weight-band FDCs; Category II discontinued.
7. DOTS = political commitment, quality diagnosis, drug supply, directly observed treatment, monitoring/recording.
8. TB is notifiable in India (2012); every provider must notify via Nikshay.
9. Nikshay Poshan Yojana gives monthly nutritional support to all notified patients via DBT.
10. BCG protects best against miliary TB and TB meningitis; given intradermally at birth, left upper arm.
11. India aims to eliminate TB by 2025; global SDG/End TB target is 2030 (< 1 case/lakh).
12. Ethambutol → optic neuritis; INH → neuropathy (give pyridoxine); rifampicin → orange secretions + enzyme induction.