IM27.1-18 | Tuberculosis — Glossary

The current NTEP daily regimen for drug-sensitive TB: 2 months of isoniazid (H), rifampicin (R), pyrazinamide (Z), and ethambutol (E) in the intensive phase, followed by 4 months of isoniazid, rifampicin, and ethambutol in the continuation phase; all doses are daily and weight-band adjusted.

The property of retaining carbol fuchsin stain after decolourisation with acid-alcohol, characteristic of mycobacteria due to their high mycolic acid content; demonstrated by the Ziehl-Neelsen (ZN) stain.

An enzyme produced by activated lymphocytes; levels >40 IU/L in pleural fluid have sensitivity ~92% and specificity ~90% for tuberculous pleuritis in the Indian context; also elevated in CSF in TB meningitis; the most practically useful bedside biochemical marker for pleural TB.

Standardised quantitative reporting for sputum AFB smear: negative (0/100 fields), scanty (1–9/100 fields, report exact count), 1+ (10–99/100 fields), 2+ (1–10 AFB/field in ≥50 fields), 3+ (>10 AFB/field in ≥20 fields); higher grades correlate with greater infectiousness.

The inability to mount a delayed hypersensitivity response to tuberculin despite true sensitisation; caused by severe immunosuppression (HIV CD4 <200, malnutrition, miliary TB, corticosteroids); produces false-negative TST — critical pitfall that may lead to missed LTBI or active TB diagnosis.

Loss of the normal fullness of the infraclavicular fossa visible on inspection of the chest, caused by upper lobe fibrosis and volume loss from healed or active post-primary TB; one of the earliest and subtlest inspection signs of pulmonary TB.

A live attenuated vaccine derived from M. bovis, developed by Calmette and Guérin; given intradermally at birth under India's Universal Immunisation Programme; highly protective against childhood meningeal and miliary TB (70–80%) but variable efficacy against adult pulmonary TB.

A diarylquinoline anti-TB drug that inhibits mycobacterial ATP synthase; the first new anti-TB drug class approved in 40 years; used in MDR-TB and XDR-TB regimens; key risk is QT prolongation — mandatory baseline and monthly ECG monitoring.

A false conversion observed in TST: in elderly or remotely sensitised individuals with waned TST reactivity, the first test may be negative, but the act of testing restores immune memory ('boosts' it), causing the second test 1–4 weeks later to be positive; this is not a new infection but an amnestic immune response.

Bedaquiline + Pretomanid + Linezolid; a 26-week (6-month) all-oral regimen for XDR-TB and treatment-intolerant or non-responsive MDR-TB; endorsed by WHO 2022; a paradigm shift from injection-based regimens.

An abnormal auscultatory finding characterised by loud, blowing breath sounds with equal inspiratory and expiratory duration and a distinct gap between them; indicates open consolidation (patent bronchus within consolidated lung enhances sound transmission from central airways); associated with increased TVF, dull percussion, and whispered pectoriloquy.

Involuntary flexion of the knees and hips when the patient's neck is passively flexed; indicates meningeal irritation; elicited alongside Kernig's sign in the neurological examination of patients with suspected meningitis.

A form of coagulative necrosis with a cheese-like gross appearance, characteristic of tuberculosis; histologically shows amorphous eosinophilic material with no visible cellular architecture, composed of dead macrophages and necrotic debris.

The brand-agnostic name for Xpert MTB/RIF in India's NTEP programme; a fully automated real-time PCR assay detecting M. tuberculosis complex DNA and rifampicin resistance mutations simultaneously in approximately 90–120 minutes; first-line diagnostic test for all presumptive TB under NTEP 2020.

Yellowish-grey discrete 1–2 mm lesions visible on fundoscopy in the choroid of the eye; pathognomonic of miliary (haematogenous) tuberculosis; present in 10–20% of miliary TB cases; their presence confirms disseminated disease.

A collection of pus lacking the usual signs of acute inflammation (warmth, redness, tenderness) because the causative organism (M. tuberculosis) elicits a predominantly granulomatous rather than neutrophilic response; characteristic of TB lymphadenitis and skeletal TB.

A dumbbell-shaped TB abscess formed when a deep collection in lymph nodes breaks through the deep fascia, creating a superficial component communicating with the deep component through a narrow fascia defect — the shape resembles a collar stud; most common in the neck from TB cervical lymphadenitis.

Rifampicin is a potent inducer of hepatic cytochrome P450 enzymes (CYP3A4, CYP2C9); this critically reduces plasma concentrations of oral contraceptives (OCP failure), nevirapine (ART failure), warfarin (INR drop), corticosteroids, and many other drugs — clinically important drug interactions requiring substitution or dose adjustment.

The WHO-endorsed operational strategy for TB control comprising five components: political commitment, quality bacteriological services, standardised supervised treatment, drug supply management, and monitoring and evaluation; ensures each dose is observed by a trained supporter.

Tiny aerosol particles (1–5 μm) containing 1–3 viable M. tuberculosis bacilli, generated by coughing, sneezing, or speaking; remain suspended in air for hours; the exclusive vehicle of TB transmission.

Laboratory testing to determine which anti-TB drugs a given M. tuberculosis isolate is susceptible to; methods include phenotypic (growing organism in the presence of drugs at defined concentrations) and genotypic (PCR-based detection of resistance mutations, as in CBNAAT and LPA).

Hepatotoxicity caused by ATT drugs (primarily isoniazid, rifampicin, pyrazinamide); defined as ALT >3× ULN with symptoms or >5× ULN without symptoms; management requires stopping all hepatotoxic ATT and sequential reintroduction after enzyme normalisation.

A first-line bacteriostatic anti-TB drug that inhibits arabinosyl transferase (arabinogalactan cell wall synthesis); primary role is prevention of resistance selection; key adverse effect is optic neuritis (reduced visual acuity, red-green colour vision loss) — requires monthly visual monitoring.

A single tablet containing multiple anti-TB drugs in standardised doses adjusted by weight band; used in NTEP to simplify treatment, prevent monotherapy, and reduce the risk of selective drug pressure; available as HRZE (four-drug intensive phase) and HRE (three-drug continuation phase) formulations.

The combination of the primary lung parenchymal lesion (Ghon focus, usually in the middle/lower zones) and ipsilateral hilar/paratracheal lymphadenopathy, formed during primary TB infection in childhood.

A sharp angular kyphosis (hump) at the thoracolumbar junction resulting from vertebral collapse in Pott's disease; the anterior elements of the involved vertebrae collapse, producing the angular deformity that is pathognomonic of spinal TB.

An organised aggregate of activated macrophages and epithelioid cells surrounded by lymphocytes, the characteristic immunological lesion of TB; central caseous necrosis distinguishes TB granuloma from non-caseating granulomas of sarcoidosis.

A cytokine produced by activated Th1 CD4+ T lymphocytes that is central to anti-TB immunity; activates macrophages to produce reactive oxygen species and nitrogen species for intracellular mycobacterial killing; the basis of IGRA (interferon-gamma release assay) testing.

A blood test measuring IFN-γ release by T lymphocytes in response to M. tuberculosis-specific antigens (ESAT-6, CFP-10); more specific than TST in BCG-vaccinated populations; not affected by BCG vaccination; cannot distinguish LTBI from active TB; used for LTBI screening before immunosuppressive therapy.

A paradoxical clinical worsening occurring when ART is initiated during TB treatment in HIV-positive patients; results from recovery of immune function mounting a stronger inflammatory reaction to TB antigens; can present with new or worsening lymphadenopathy, fever, or respiratory deterioration.

A first-line bactericidal anti-TB drug that inhibits mycolic acid synthesis by targeting the KatG/InhA pathway; a prodrug activated by bacterial catalase-peroxidase; key adverse effects include peripheral neuropathy (prevented by pyridoxine), hepatotoxicity, and drug-induced lupus; inhibits CYP2C19.

Chemoprophylaxis with isoniazid to prevent progression of latent TB infection to active disease; the NTEP standard for children <5 years who are household contacts of DS-TB cases and have been evaluated to have no active TB: isoniazid 10 mg/kg/day (max 300 mg/day) for 6 months.

A sign of meningeal irritation elicited by flexing the hip to 90° then attempting to extend the knee; resistance and pain indicate meningeal irritation; positive in TB meningitis, bacterial meningitis, and subarachnoid haemorrhage.

The band of resonance over the upper trapezius muscle, between the neck and the shoulder, representing the resonance of the lung apex; dullness or diminishment of Kronig's isthmus indicates upper lobe disease (TB, malignancy, apical consolidation) and is an important percussion finding in apical TB.

A state of persistent immune response to M. tuberculosis antigens without evidence of clinically active disease; characterised by positive TST/IGRA, normal chest X-ray, and no symptoms; carries a 5–10% lifetime risk of reactivation in immunocompetent adults.

PCR-based strip hybridisation assay for simultaneous detection of drug resistance mutations; MTBDRplus detects rpoB (rifampicin), katG and inhA (isoniazid) resistance; MTBDRsl detects fluoroquinolone (gyrA/gyrB) and aminoglycoside (rrs) resistance for pre-XDR/XDR characterisation.

Interruption of TB treatment for ≥2 consecutive months; an adverse treatment outcome under NTEP; patients returning after LTFU from DR-TB treatment require fresh DST before re-treatment due to risk of resistance amplification.

An egg-based solid culture medium for M. tuberculosis; colonies appear after 4–8 weeks as buff-coloured, rough, raised, warty (breadcrumb-like) growths; confirmatory medium for culture and DST in NTEP laboratories.

Tuberculosis caused by M. tuberculosis resistant to at least both isoniazid and rifampicin; the most clinically important form of drug resistance; requires second-line drug regimens for 18–20 months; increasing rates driven by incomplete or inadequate prior treatment.

Haematogenous dissemination of M. tuberculosis producing a chest X-ray pattern of uniform 1–2 mm nodules bilaterally, resembling millet seeds; associated with severe immunosuppression and young children; high mortality if untreated.

TB caused by strains resistant to at least isoniazid and rifampicin simultaneously — the two most bactericidal first-line drugs; requires second-line regimens of at least 18–20 months; approximately 119,000 cases per year in India.

A liquid culture system for M. tuberculosis using fluorescent oxygen-sensing technology; detects growth in 10–14 days (versus 4–8 weeks on solid LJ medium); used for rapid culture confirmation and liquid DST in NTEP reference laboratories.

The principal causative organism of human tuberculosis; an obligate aerobic, slow-growing, acid-fast bacillus with a mycolic-acid-rich cell wall that confers resistance to desiccation, acid-alcohol decolourisation, and many antibiotics.

Very-long-chain fatty acids (C60–C90) that form the outer layer of the mycobacterial cell wall, conferring acid-fastness, resistance to intracellular killing, and low permeability to many antibiotics.

The Government of India's mandatory web-based national TB notification and patient management portal; all TB patients (public and private sector) must be notified within 24 hours of diagnosis; triggers patient support mechanisms including Ni-kshay Poshan Yojana.

A government of India nutritional support scheme for all TB patients notified on Nikshay; provides ₹500 per month during treatment to address the high prevalence of malnutrition among TB patients and improve treatment adherence and outcomes.

India's national web-based TB patient management and notification portal under NTEP; all TB cases (public and private sector) must be notified on Nikshay; enables patient tracking and Ni-kshay Poshan Yojana nutritional support delivery.

India's national TB control programme, renamed from RNTCP in 2020 to reflect the goal of TB elimination by 2025; delivers free daily FDC-based treatment, mandatory CBNAAT diagnostics, and Ni-kshay digital notification.

The National Tuberculosis Elimination Programme's primary case-finding tool: any person with at least one of cough ≥2 weeks, fever ≥2 weeks, significant weight loss, or drenching night sweats is classified as presumptive TB and referred for CBNAAT testing.

A dose-dependent adverse effect of ethambutol manifesting as reduced visual acuity, impaired red-green colour discrimination, and central scotomata; largely reversible if detected early; mandates monthly visual acuity and colour vision testing in all patients receiving ethambutol.

Adenosine deaminase >40 IU/L in pleural fluid is the standard diagnostic threshold for TB pleuritis; sensitivity approximately 92%, specificity approximately 90% for TB vs other causes of lymphocyte-predominant effusion in high-burden settings; ADA >70 IU/L is strongly suggestive.

Crepitations (crackling breath sounds) that appear or increase after the patient coughs; highly specific for TB cavitation — the cough displaces secretions within the cavity wall, unmasking the crackling of moist surfaces; should be actively sought in every TB examination.

Tuberculosis of the spine — most commonly affecting the lower thoracic and upper lumbar vertebrae (D10–L2); characterised by disc space loss, vertebral end-plate destruction, and paraspinal cold abscess; may cause Pott's paraplegia from cord compression.

Any person who presents with symptoms or signs suggestive of tuberculosis but has not yet received a bacteriological or pathological confirmation; the NTEP four-symptom screen (cough, fever, night sweats, weight loss ≥2 weeks) is used to identify presumptive TB cases.

The standardised tuberculin antigen used in the Mantoux test; derived from heat-sterilised, concentrated filtrate of M. tuberculosis culture; 5 TU (tuberculin units) per 0.1 mL is the standard dose in India's NTEP.

A first-line anti-TB drug active in acidic environments within macrophage phagolysosomes; essential for the sterilising activity of the 2-month intensive phase; key adverse effects include hepatotoxicity, hyperuricaemia, arthralgia, and photosensitivity.

A CBNAAT result indicating that M. tuberculosis was detected but the rifampicin resistance determination was technically indeterminate (neither confidently susceptible nor resistant); requires repeat testing; should be managed as potential RR-TB while awaiting repeat/culture DST result.

The cornerstone sterilising first-line anti-TB drug; inhibits bacterial RNA polymerase (rpoB subunit); causes harmless orange-red discolouration of body fluids; a potent CYP3A4/2C9 inducer — reduces efficacy of oral contraceptives, nevirapine, warfarin, and many other drugs.

A sputum AFB smear result showing 1–9 acid-fast bacilli per 100 microscopic fields; classified as positive (low bacillary load); requires reporting the exact count; patient is potentially infectious; CBNAAT or culture required for species confirmation and DST.

The combination of silicosis (from occupational silica dust exposure) and TB; silica particles impair macrophage function and facilitate intracellular TB survival, making workers in dusty trades (stone-cutting, sandblasting, mining) at particularly high risk; treatment response is poor.

The dullest percussion note in clinical medicine, with a solid, 'wooden' quality; characteristic of pleural effusion (fluid completely attenuates the percussion wave); distinguishable from the simple dullness of consolidation or the muffled note of pericardial effusion.

The palpable vibration transmitted to the chest wall when the patient phonates (says 'ninety-nine'); increased over consolidated lung (better sound conduction through solid tissue) and decreased/absent over pleural effusion or collapse.

Treatment given to individuals with LTBI to prevent progression to active TB; current NTEP options include 6 months of daily isoniazid (6H) or the newer 3HP regimen (weekly isoniazid + rifapentine for 3 months); mandatory for all HIV-positive individuals after ruling out active TB.

Antibody-detection tests for TB (various commercial immunoassays detecting antibodies to TB antigens); explicitly NOT recommended by WHO or NTEP for TB diagnosis; sensitivity and specificity are unacceptably variable; use may lead to overdiagnosis and inappropriate treatment; banned from the NTEP programme.

Sputum smear-positive result at month 5 or later during standard DS-TB treatment; mandates CBNAAT and DST; if rifampicin resistance is confirmed, the patient is transferred to the DR-TB pathway.

The single most probable diagnosis that best explains the entire clinical picture, based on the integration of history, examination, epidemiology, and prior probability; the working diagnosis drives immediate management decisions while the full differential is being evaluated through investigations.

MDR-TB with additional resistance to any fluoroquinolone and at least one of bedaquiline or linezolid; extremely difficult to treat with available drugs; requires highly individualised regimens.

MDR-TB with additional resistance to any fluoroquinolone and at least one of bedaquiline or linezolid (WHO 2021 revised definition); treated with the BPaL regimen (bedaquiline + pretomanid + linezolid) for 26 weeks.

A WHO-endorsed CBNAAT platform by Cepheid; simultaneously detects M. tuberculosis-specific rpoB gene and probes five regions for rifampicin resistance mutations; sensitivity ~88% for smear-positive, ~67% for smear-negative pulmonary TB; results available in approximately 2 hours.