tuberculosis

Mycobacterium tuberculosis

The organism that causes tuberculosis (TB), primarily responsible for the disease.

Type of bacterium for M. tuberculosis

Slow-growing, aerobic, acid-fast bacillus (AFB).

Main organisms in the M. tuberculosis complex

M. tuberculosis, M. bovis, M. africanum, M. canettii.

Transmission method for pulmonary TB

By airborne droplet nuclei produced when an infectious person coughs, sneezes, speaks, sings, or shouts.

Prolonged exposure requirement for TB transmission

Usually yes; prolonged or repeated exposure carries greater risk, while brief casual contact has relatively low risk.

Infectiousness of extrapulmonary TB

Generally not infectious except when TB involves the larynx.

Transmission routes for TB

Not transmitted by sharing food, toilets, or utensils.

Incubation period after TB infection

Approximately 2–12 weeks.

Post-infection outcomes of TB

Individuals may develop active TB or remain with latent TB infection (LTBI).

Longevity of latent TB

Can persist for many years or decades before reactivation.

Infectiousness of a person with latent TB

No; they have no symptoms and are not infectious.

Percentage of infected people developing active TB

Approximately 5–10%.

Condition increasing risk of active TB

HIV infection.

Environmental factors increasing TB transmission

Poor ventilation and overcrowding.

First step in TB pathogenesis

Inhalation of airborne droplet nuclei that reach the terminal bronchioles and alveoli.

Cells ingesting TB bacilli

Alveolar macrophages.

Outcome if macrophages cannot destroy M. tuberculosis

The bacilli multiply intracellularly and spread to regional lymph nodes and sometimes through the bloodstream.

Formation after cell-mediated immunity develops in TB

Granulomas.

Composition of TB granulomas

Activated macrophages, lymphocytes, and central caseous necrosis.

Location of viable TB bacilli during latent infection

Within granulomas.

Most common form of TB

Pulmonary TB.

Classic symptom of pulmonary TB

Persistent cough lasting longer than 2 weeks.

Type of cough in pulmonary TB

Productive cough; haemoptysis may also occur.

Constitutional symptoms of TB

Fever, night sweats, loss of appetite, weight loss, and fatigue.

Respiratory symptoms in pulmonary TB

Persistent/productive cough, haemoptysis, and chest pain.

Physical examination findings in pulmonary TB

Crackles, dullness to percussion, bronchial breathing, and increased vocal fremitus.

First-line diagnostic test for TB

Xpert MTB/RIF Ultra on sputum or an appropriate clinical specimen.

Detection by Xpert MTB/RIF Ultra

Mycobacterium tuberculosis and rifampicin resistance.

Purpose of AFB smear

Detection of acid-fast bacilli.

Role of mycobacterial culture in TB diagnosis

To isolate M. tuberculosis and allow further testing, including drug susceptibility testing.

Tests detecting latent TB infection

Mantoux (Tuberculin Skin Test) and Interferon-Gamma Release Assays (IGRAs).

Common imaging for pulmonary TB

Chest X-ray/radiograph.

Important additional test in TB patients

HIV testing.

Urine LAM purpose

Detection of TB in selected HIV-positive patients with advanced immunosuppression.

Important extrapulmonary manifestations of TB

Lymphadenopathy, pleural effusion, TB meningitis, pericarditis, bone/joint TB, genitourinary TB, and abdominal TB.

What is Pott disease?

Spinal tuberculosis.

What is miliary TB?

Disseminated tuberculosis involving multiple organs.

Pulmonary complications of TB

Pleural effusion, pneumothorax, empyema, massive haemoptysis, bronchiectasis, chronic respiratory failure, and cor pulmonale.

Extrapulmonary complications of TB

TB meningitis, TB pericarditis, spinal TB, and disseminated/miliary TB.

Definition of rifampicin-resistant TB (RR-TB)

TB resistant to rifampicin, with or without resistance to other first-line drugs.

Definition of MDR-TB

TB resistant to at least isoniazid and rifampicin.

Definition of pre-XDR-TB

MDR/RR-TB with additional resistance to any fluoroquinolone.

Definition of XDR-TB

Resistance to rifampicin, isoniazid, any fluoroquinolone, and at least one additional Group A drug such as bedaquiline or linezolid.

Standard regimen for drug-susceptible TB

2HRZE/4HR.

Meaning of 2HRZE/4HR

2 months: isoniazid + rifampicin + pyrazinamide + ethambutol; followed by 4 months: isoniazid + rifampicin.

Intensive phase of drug-susceptible TB treatment

2 months of HRZE.

Continuation phase in TB treatment

4 months of HR.

Reason for administering pyridoxine with isoniazid

To help prevent isoniazid-associated peripheral neuropathy in patients at increased risk.

Who is at increased risk of isoniazid-induced neuropathy?

People with HIV, pregnant/breastfeeding women, diabetes, malnutrition, CKD, and alcohol dependence.

Pyridoxine dose mentioned in notes

25–50 mg orally daily.

TB drug associated with visual toxicity

Ethambutol.

Monitoring during TB treatment

Clinical improvement, adherence, adverse effects, sputum conversion, liver function, renal function, and visual acuity.

When are corticosteroids recommended as adjunctive treatment?

In TB meningitis and TB pericarditis.

Drugs used in modern drug-resistant TB regimens

Bedaquiline, linezolid, pretomanid, moxifloxacin, and, in selected patients, delamanid.

What is BPaLM?

Bedaquiline + Pretomanid + Linezolid + Moxifloxacin.

WHO-recommended preventive treatment options for LTBI

3HP: weekly isoniazid + rifapentine for 3 months; 3HR: daily isoniazid + rifampicin for 3 months; 4R: daily rifampicin for 4 months; 6H: daily isoniazid for 6 months.