Tuberculosis in detail PSM

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Tuberculosis - PSM (Preventive and Social Medicine)

Source: Park's Textbook of Preventive and Social Medicine

1. DEFINITION AND INTRODUCTION

Tuberculosis is a specific infectious disease caused by Mycobacterium tuberculosis. It primarily affects the lungs (pulmonary TB) but can also affect intestine, meninges, bones and joints, lymph glands, skin, and other tissues. The disease is usually chronic with varying clinical manifestations. Bovine TB (caused by M. bovis) can also be transmitted to humans.

2. EPIDEMIOLOGY - GLOBAL (Problem Statement)

About one-third of the global population is infected asymptomatically; 5-10% will develop clinical disease during their lifetime
Annual risk of TB infection in high burden countries: 0.5-2%
A patient with infectious pulmonary TB can infect 10-15 persons per year
Globally, an estimated 10 million people had TB in 2019
1.2 million deaths among HIV-negative people + 208,000 deaths among HIV-positive people
Age-sex distribution: Men ≥15 years - 56%; Women - 32%; Children <15 years - 12%
Geographic distribution (2019): South-East Asia 44%, Africa 25%, Western Pacific 18%
India has the highest burden at 26% of global cases, followed by Indonesia (8.5%) and China (8.4%)
MDR/RR-TB: 3.3% of new cases and 18% of previously treated cases
Estimated 465,000 incident cases of rifampicin-resistant TB; 78% had MDR-TB
India (27%), China (14%), Russian Federation (8%) had the largest MDR-TB burdens
Treatment success rate: 85% for TB; 57% for MDR/RR-TB; 76% for TB/HIV co-infection

3. EPIDEMIOLOGY - INDIA

India accounts for 26% of global TB cases (highest in the world)
India has 17% of the global gap between diagnosed and estimated cases
Paediatric TB accounts for approximately 10% of all cases
India is among the top 5 countries accounting for more than half the global diagnostic gap (with Nigeria, Indonesia, Pakistan, Philippines)

4. AGENT FACTORS

Feature	Detail
Organism	Mycobacterium tuberculosis (Koch's bacillus)
Type	Acid-fast bacillus (AFB); obligate aerobe
Bovine type	M. bovis - zoonotic, can infect humans
Infectivity	High
Pathogenicity	Moderate - only 5-10% of infected develop disease
Virulence	Varies with strain
Drug resistance	MDR-TB (resistant to INH + Rifampicin); XDR-TB

5. HOST FACTORS

Increased susceptibility:

Age: Children (primary infection), young adults (post-primary)
Sex: Males more affected (56% of global cases)
Malnutrition - the most important predisposing factor
Diabetes mellitus - 2-3 times higher risk
HIV/AIDS - most powerful risk factor (40x increased risk); annual risk of TB in HIV-positive persons is 5-15%
Silicosis - markedly increases risk
Steroid therapy / immunosuppression
Alcoholism and smoking
Overcrowding and poverty
Occupational exposure (healthcare workers, miners)

Protective factors:

BCG vaccination
Previous infection (relative protection)
Genetic factors (certain HLA types)

6. ENVIRONMENTAL FACTORS

Overcrowding: The most important environmental factor; facilitates droplet transmission
Poor ventilation: Increases concentration of infectious droplets
Low socioeconomic status: Poor nutrition, overcrowding, lack of access to care
Urbanization: Slum dwellings, migration
Sunlight and UV radiation: Kill bacilli (hence, ventilation and sunlight are protective)

7. MODES OF TRANSMISSION

Droplet infection (most common route) - inhalation of droplet nuclei expelled by sputum-positive patients during coughing, sneezing, talking, or singing. Droplet nuclei (1-5 microns) remain suspended in air for hours.
Droplet contact - direct contact with fresh droplets on mucous membranes (less common)
Dust infection - dried sputum on floors/surfaces resuspended as dust (less important)
Direct inoculation - skin (rare, laboratory/pathology workers)
Ingestion - bovine TB via infected milk (M. bovis) - causes intestinal/mesenteric TB
Congenital - transplacental (extremely rare)

The most dangerous source is the sputum-positive (smear-positive) pulmonary TB patient.

8. NATURAL HISTORY OF TUBERCULOSIS

Stages

Exposure - contact with an infectious case
Infection (Latent TB / LTBI) - bacilli establish infection; no clinical disease. Tuberculin test becomes positive (conversion occurs 4-8 weeks post-infection). The majority (~90-95%) remain in latent state lifelong.
Disease - Only 5-10% of infected individuals develop active disease
- Primary TB: First infection, often in children; heals spontaneously in most
- Post-primary (Reactivation) TB: Reactivation of dormant foci due to reduced immunity

Spectrum of infection and disease

Stage	Description
Exposed, not infected	No infection despite exposure
LTBI	Infected, tuberculin +ve, no disease
Primary TB	First episode; usually self-limiting
Progressive primary	Direct progression to active disease (children, immunocompromised)
Reactivation TB	Dormant foci reactivate; most adult cases
Miliary/Disseminated TB	Haematogenous spread

9. EPIDEMIOLOGICAL INDICES (Parameters for Measurement)

Incidence - number of new and recurrent (relapse) episodes per year
Prevalence - number of TB cases (all forms) at a given point in time (best practical index for case load)
Mortality - deaths caused by TB in HIV-negative people (per ICD-10)
Case fatality rate - risk of death among those with active TB
Case notification rate - new and recurrent episodes notified to WHO per 100,000 population per year
Case detection rate - notifications of new and relapse cases ÷ estimated incidence in the same year
Prevalence of drug-resistant cases - proportion excreting drug-resistant bacilli
Prevalence of infection - percentage with positive tuberculin test (most important epidemiological index)
- Annual Risk of Tuberculosis Infection (ARTI) = the most sensitive index for monitoring trends; estimated from tuberculin survey data in children 1-9 years (unvaccinated). 1% ARTI ≈ 50-60 smear-positive cases per 100,000 population

10. CASE DEFINITIONS (Revised 2013)

Category	Definition
Presumptive TB	Person with symptoms/signs suggestive of TB (cough ≥2 weeks, etc.)
Bacteriologically confirmed TB	Positive sputum smear, culture, or WHO-approved rapid test (e.g., CB-NAAT)
Clinically diagnosed TB	No bacteriological confirmation but diagnosed by clinician based on X-ray, histology, clinical criteria, response to treatment
New case	Never treated or treated for <1 month
Relapse	Previously treated and declared cured/treatment completed; now bacteriologically confirmed again
Treatment after failure	Previously treated; smear/culture positive at month 5 or later
Treatment after LTFU	Previously treated; treatment interrupted for ≥2 months, now returns
Previously treated, unknown outcome	History of treatment, outcome unknown
Drug-resistant TB	Confirmed resistance on DST

11. DIAGNOSIS

A. Sputum Microscopy

Ziehl-Neelsen (Z-N) staining - gold standard for smear microscopy
LED Fluorescence Microscopy (LEDFM) - more sensitive than ZN, comparable to conventional fluorescence microscopy; recommended as replacement
Two specimens collected: spot-early morning or spot-spot

B. Culture

MGIT (Mycobacteria Growth Indicator Tube) - liquid culture; faster than solid media
LJ (Lowenstein-Jensen) medium - solid culture; takes 4-8 weeks
More sensitive and specific than smear

C. Rapid Molecular Diagnostics

CB-NAAT (Cartridge-Based Nucleic Acid Amplification Test / GeneXpert MTB/RIF):
- Detects M. tuberculosis DNA and rifampicin resistance (rpoB gene mutations)
- Results in 90 minutes
- Used for: DR-TB presumption, PLHIV, children, EPTB, smear-negative cases
Line Probe Assay (LPA):
- First-line LPA: detects resistance to Rifampicin (rpoB) and Isoniazid (katG, inhA)
- Second-line LPA: detects fluoroquinolone resistance (gyrA, gyrB) and second-line injectable resistance (rrs, eis)
NAAT - detects M. tuberculosis and rifampicin resistance; used for EPTB and key populations

D. Tuberculin Test (Mantoux Test)

Discovered by Von Pirquet in 1907
0.1 mL of PPD (Purified Protein Derivative) - 1 TU or 2 TU - injected intradermally
Read at 48-72 hours - measure induration (not erythema)
Interpretation:
- ≥10 mm induration = positive in general population
- ≥5 mm = positive in immunocompromised (HIV, steroids)
- Positive = evidence of past or present infection with M. tuberculosis
Uses: Epidemiological surveys (prevalence of infection, ARTI estimation); identifying LTBI; diagnosing TB in children
Limitations: Cannot distinguish between active disease and latent infection; false positive with NTM and BCG vaccination; false negative in severe immunosuppression (anergy)

E. Chest X-Ray

Useful for: smear-negative pulmonary TB, TB in children, pleural/pericardial effusion, miliary TB
Not routinely indicated in smear-positive cases (diagnosis already confirmed)
Essential for miliary TB diagnosis

F. Diagnostic Algorithm (NTEP)

For presumptive TB: Sputum smear (ZN/LEDFM) x 2 specimens

If 1st smear positive and no DR-TB risk: microscopically confirmed TB
If 1st smear negative: CXR + 2nd specimen for smear AND CB-NAAT
CB-NAAT result determines DS-TB vs DR-TB categorization

12. TREATMENT

Pre-treatment Counseling and Evaluation

Explain: type of disease, mode of spread, duration, dosage, side effects, importance of adherence
Screen for comorbidities: diabetes, liver/renal disease, neurological disorders
Assess for tobacco and alcohol use
HIV testing mandatory in all TB cases - to ensure ART + co-trimoxazole preventive therapy

Anti-tuberculosis Drugs

Bactericidal Drugs:

Drug	Key Features
Isoniazid (INH/H)	Most powerful anti-TB drug; active on intra- and extracellular bacilli; most active on rapidly multiplying bacilli; penetrates CSF; given as single dose (peak serum level important, not sustained level); Side effects: peripheral neuropathy (prevented by pyridoxine 10-20 mg/day), hepatotoxicity, blood dyscrasias
Rifampicin (R)	Highly bactericidal; sterilizing activity; acts on semi-dormant/persister bacilli; broad spectrum; induces hepatic enzymes; Side effects: hepatotoxicity, orange discoloration of body fluids, drug interactions
Pyrazinamide (Z)	Active against slow-multiplying intracellular bacilli; unaffected by other drugs; increases sterilizing ability of rifampicin; incorporated in short-course regimens; achieves high CSF levels (used in TB meningitis); Side effects: hepatotoxicity, hyperuricaemia
Streptomycin (S)	Bactericidal; acts only on rapidly multiplying extracellular bacilli; no action on persisters; does NOT penetrate cell walls or meninges/pleura; IM injection (disadvantage); Side effects: vestibular damage, nystagmus, renal damage

Bacteriostatic Drugs:

Drug	Key Features
Ethambutol (E)	Bacteriostatic; inhibits mycolic acid synthesis; used to prevent resistance; Side effect: retrobulbar neuritis (dose-dependent; check visual acuity)
Thioacetazone (T)	Cheap; used in some regimens (not in HIV due to severe skin reactions)

Standard Treatment Regimens (NTEP - Daily FDC)

Under NTEP, the thrice-weekly intermittent regimen has been replaced with daily fixed-dose combination (FDC) regimen.

Drug-Sensitive TB (Daily FDC):

Phase	Duration	Drugs
Intensive Phase (IP)	2 months	H + R + Z + E (2HRZE)
Continuation Phase (CP)	4 months	H + R (4HR)
Total	6 months

Weight-band based dosing
Change in weight bands effective upon crossing weight bands
Pyridoxine 10 mg/day to all children on INH therapy

Nikshay: All patients must be registered on the Nikshay portal (IT platform for TB notification and monitoring). All events from notification to treatment outcome are recorded.

Follow-up of Treatment

Clinical: Monthly interval; assess chest symptoms, weight gain
Sputum smear microscopy: At end of intensive phase and end of treatment
Long-term: 6, 12, 18, and 24 months after treatment completion
Negative smear at end of IP = good prognosis

13. TREATMENT OUTCOMES (WHO Definitions)

Outcome	Definition
Cured	Bacteriologically confirmed TB, smear/culture negative in last month of treatment AND at ≥1 previous occasion
Treatment completed	Completed treatment without evidence of failure but no smear/culture records available
Treatment failed	Sputum smear/culture positive at month 5 or later during treatment
Died	Death for any reason before or during treatment
Lost to follow-up (LTFU)	Did not start treatment or treatment interrupted for ≥2 consecutive months
Not evaluated	No outcome assigned (includes transferred out)
Treatment success	Cured + Treatment completed

14. DRUG-RESISTANT TUBERCULOSIS (DR-TB)

Definitions

Type	Resistance Pattern
Mono-resistant	Resistant to one first-line drug
Poly-resistant	Resistant to >1 first-line drug (not INH + RIF together)
MDR-TB	Resistant to INH + Rifampicin (± others)
RR-TB	Rifampicin resistant (detected by any method)
Pre-XDR-TB	MDR/RR-TB + resistance to any fluoroquinolone
XDR-TB	MDR/RR-TB + resistance to fluoroquinolone + ≥1 second-line injectable (amikacin, kanamycin, capreomycin)
TDR-TB	Totally drug-resistant (resistant to all tested drugs)

Causes of DR-TB

Irregular/incomplete treatment
Inadequate regimens
Poor drug quality
Malabsorption
Transmission of resistant strains

DR-TB Treatment Regimens (NTEP)

Regimen	Drugs	Duration
H mono/poly DR-TB	Lfx + R + E + Z	6 months
Shorter MDR-TB regimen	(4-6 months IP) Mfx + Km/Am + Eto + Cfz + Z + H + E → (5 months CP) Mfx + Cfz + Z + E	9-11 months
All-oral longer MDR-TB regimen	Bdq (6m) + Lfx + Lzd + Cfz + Cs	18-20 months

New drugs: Bedaquiline (Bdq) and Delamanid (Dlm) available under expanded access in NTEP since 2016.

Inclusion criteria for Bdq/Dlm: Age >6 years, MDR/RR-TB, non-pregnant

Exclusion: Pregnancy, uncontrolled arrhythmia, QTcF ≥500 ms at baseline, risk factors for Torsade de Pointes

15. THE CONTROL OF TUBERCULOSIS

Tuberculosis control = reduction in prevalence and incidence of disease in the community

Two fundamental components:

Curative component - Case finding + Treatment
Preventive component - BCG vaccination

"The most powerful weapon is the combination of case-finding and treatment."

Case Finding

a. Passive case finding: Over 60% of pulmonary TB patients seek care on their own due to chest symptoms. This is the most fertile group for case-finding.

b. Intensified TB Case Finding (ICF): Provider-initiated; targets clinically, socially, and occupationally vulnerable groups. Screening approaches:

Community screening:
- Mobile/fixed facility screening
- Door-to-door household screening
Institutional screening:
- In health care facilities (hospital outpatients, inpatients)
- In prisons, mines, shelters

Priority vulnerable groups for ICF:

Contacts of confirmed TB cases (especially household contacts)
PLHIV (People Living with HIV)
Diabetics
Prisoners
Healthcare workers
Migrants and homeless persons
Malnourished individuals

16. BCG VACCINATION

BCG (Bacillus Calmette-Guerin) = live attenuated M. bovis vaccine
Provides protection against: severe forms of childhood TB (miliary TB, TB meningitis) and leprosy
Efficacy: Varies widely (0-80%) in different studies; average ~50% against pulmonary TB; higher against disseminated/meningeal forms
Schedule in India (NIS): Given at birth or as early as possible; single dose
Route: Intradermal (0.1 mL in adults; 0.05 mL in neonates); left upper arm
Contraindications: Immunocompromised states, HIV (symptomatic), extensive skin disease
BCG scar: Considered evidence of vaccination; appears at 4-6 weeks
BCG does NOT prevent infection but prevents progression to severe disease

17. TUBERCULOSIS AND HIV

HIV is the single most powerful risk factor for TB
Annual risk of TB in HIV-positive individuals: 5-15% (vs. lifetime risk of 5-10% in HIV-negative)
TB is the most common opportunistic infection and leading cause of death in PLHIV
HIV-positive TB deaths are classified as HIV deaths under ICD-10
All TB patients must be HIV-tested
HIV-positive TB patients receive: Anti-TB drugs + ART + Co-trimoxazole preventive therapy (CPT)
ART should be started within 2-8 weeks of starting anti-TB treatment (regardless of CD4 count)
IRIS (Immune Reconstitution Inflammatory Syndrome) may occur after ART initiation

18. TUBERCULOSIS AND DIABETES

TB-DM association is significant; DM increases TB risk 2-3 times
TB can worsen glycemic control
Screening for DM in all TB patients is recommended under NTEP
Rifampicin reduces levels of oral hypoglycemic agents (drug interaction)
Treated simultaneously; both conditions should be optimally managed

19. CHILDHOOD TUBERCULOSIS

Children account for ~10-12% of global TB cases
Diagnosis is difficult (paucibacillary; sputum often unavailable)
BCG protects against severe forms
Tuberculin test is more useful in children
CB-NAAT preferred for diagnosing TB in children
Gastric lavage for AFB smear (if sputum not obtainable)
Dosage is weight-band based

20. LATENT TUBERCULOSIS INFECTION (LTBI)

~1/3 of world population has LTBI
Definition: Infected with M. tuberculosis but no active disease; tuberculin test positive
Treatment of LTBI recommended for:
- PLHIV
- Children <5 years in contact with active TB cases
- Household contacts of smear-positive cases
Regimens: INH preventive therapy (IPT) for 6 months; or 3HP (weekly INH + Rifapentine for 3 months)

21. NATIONAL TUBERCULOSIS ELIMINATION PROGRAMME (NTEP)

History

Year	Milestone
1962	National TB Programme (NTP) launched
1993	Revised National TB Control Programme (RNTCP) launched (with WHO/DOTS)
1997	RNTCP expanded nationwide
2020	Renamed as National Tuberculosis Elimination Programme (NTEP)
2025	Target: Eliminate TB by 2025 (ahead of global SDG target of 2030)

Goals of NTEP

Eliminate TB (incidence <1/million population) by 2025
Reduce TB deaths by 90% by 2025 (compared to 2015)
Reduce TB incidence by 80% by 2025
Zero catastrophic cost for TB-affected families

Key Components of NTEP (DOTS Strategy)

DOTS = Directly Observed Treatment, Short-course

Component	Details
Political commitment	Sustained government funding and support
Case detection	Through quality sputum smear microscopy (passive + intensified case finding)
Standardized treatment	Short-course chemotherapy under direct observation
Uninterrupted drug supply	Regular and uninterrupted drug supply chain
Monitoring and evaluation	Standardized recording and reporting (Nikshay)

NTEP Infrastructure

District TB Centre (DTC): Programme management at district level; headed by District TB Officer (DTO)
TB Unit (TBU): One per 5 lakh population; linked to several DMCs
Designated Microscopy Centre (DMC): One per 1 lakh urban / 50,000 rural population; performs sputum smear microscopy
Drug-Resistant TB Centre (DRTBC): Manages all DR-TB patients; provides culture, DST, and treatment
National Reference Laboratory (NRL): Quality assurance; culture and DST
Intermediate Reference Laboratory (IRL): Intermediate level quality control
Nikshay: Web-based case-based surveillance platform for TB notification and tracking

Nikshay Poshan Yojana

Financial incentive scheme under NTEP
TB patients receive ₹500 per month as nutritional support throughout treatment
Transferred directly to bank account via DBT (Direct Benefit Transfer)

PM TB Mukt Bharat Abhiyan

Launched 2022
Community-based support to TB patients (Ni-kshay Mitras - adopters who provide nutritional and other support)
Goal: Accelerate TB elimination

22. DOTS-PLUS (for MDR-TB)

DOTS-Plus = DOTS strategy adapted for MDR-TB
Uses second-line drugs under direct observation
Requires culture and DST facilities
Longer treatment (18-24 months for MDR; up to 24 months for XDR)
Implemented through DRTBC

23. END TB STRATEGY (WHO, 2015-2035)

Targets by 2030 (SDG-aligned):

90% reduction in TB deaths (vs. 2015)
80% reduction in TB incidence
Zero catastrophic cost

Pillars:

Integrated, patient-centred care and prevention
Bold policies and supportive systems
Intensified research and innovation

24. TB SURVEILLANCE INDICATORS

Indicator	Definition/Benchmark
ARTI (Annual Risk of TB Infection)	Most sensitive epidemiological index; estimated from tuberculin surveys in 1-9 year old children; 1% ARTI ≈ 50-60 sputum-positive cases/100,000
Case detection rate	Notifications ÷ Estimated incidence
Treatment success rate	Target: ≥90%
LTFU rate	Target: <5%
MDR-TB treatment success	Target: ≥75%

25. PREVENTION AND CONTROL - SUMMARY

Approach	Measures
Primary prevention	BCG vaccination; Health education; Improved nutrition; Reduction of overcrowding; Improved ventilation; Chemoprophylaxis (LTBI treatment)
Secondary prevention	Early case detection (passive + active case finding); Sputum microscopy; CB-NAAT; Rapid treatment initiation
Tertiary prevention	Prevent complications; ensure treatment completion; prevent relapse; DOTS; follow-up

Environmental measures: Improving standards of living (historically the most important driver of TB decline - preceded BCG and chemotherapy); ventilation; sunlight; reduction of overcrowding.

KEY FACTS FOR EXAM (Quick Review)

Item	Fact
Causative organism	Mycobacterium tuberculosis (Koch's bacillus)
Most important mode of transmission	Droplet infection (droplet nuclei 1-5 microns)
Most important env. factor	Overcrowding
Most powerful risk factor	HIV/AIDS
Most important predisposing factor	Malnutrition
Patients infected per year by one smear+ve case	10-15
% of infected who develop disease	5-10%
ARTI in India	1% approximately
1% ARTI corresponds to	~50-60 smear-positive cases per 100,000
Tuberculin test read at	48-72 hours
Tuberculin test discovered by	Von Pirquet (1907)
RNTCP renamed to NTEP	2020
India's TB elimination target	2025 (5 years ahead of global SDG 2030)
Standard DS-TB regimen	2HRZE + 4HR (daily FDC)
Treatment failed (definition)	Smear/culture +ve at month 5 or later
LTFU (definition)	Treatment interrupted for ≥2 consecutive months
Treatment success	Cured + Treatment completed
Nikshay Poshan Yojana	₹500/month nutritional support
Most powerful TB control weapon	Case-finding + Treatment
BCG vaccine efficacy (meningeal/miliary TB)	~80%
MDR-TB definition	Resistant to INH + Rifampicin
New drugs for MDR-TB	Bedaquiline, Delamanid
CB-NAAT result time	90 minutes
India's share of global TB burden	26%

Park's Textbook of Preventive and Social Medicine, community medicine section

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