Mycobacterial Infections

Question 1

TB transmission

Answer 1

Airborne (droplets stay airborne for hours)

From person with active TB, not latent

Question 2

TB pathophysiology

Answer 2

Acid fast bacilli in alveolus → release of acid fast bacilli into the extracellular space → cell-mediated immunity → granuloma formation (spread to lymph nodes, blood stream and other organs) → either latent (strong cellular immunity and containment) or active (poor cellular immunity, progressive disease)
Reactivation can be triggered by old age, race, steroids, HIV, malnutrition, diabetes, malignancy, smoking, immunosuppression, anti-TNF alpha

Question 3

TB presentation

Answer 3

Cough, haemoptysis or chest pain
Often asymptomatic or non-specific (fatigue, weight loss, night sweats)
20% non-pulmonary (higher in HIV +ve): lymph nodes, pleura, genito-urinary, skeletal, CNS, pericardia, peripheral cold abscess

Question 4

Diagnosis

Answer 4

CXR: upper lobe infiltrates +/- cavitation; CT more sensitive
ZN stain and culture
PCR
Tuberculin skin test
Interferon-gamma
Biopsy demonstrating granulomis

Question 5

Treatment principles

Answer 5

Send to lab before initiating
Never use a single drug or add a single drug to a failing regime
Treat for at least six months
Ensure compliance - DOTS if necessary
Watch hepatic/renal function
Usually smear negative (non-infectious) after 2 weeks
CXR at end

Question 6

First line drugs

Answer 6

Rifampicin (bactericidal); SE discolouration of urine/tears, hepatic enzyme induction
Isoniazid (bactericidal); SE: hepatitis, peripheral neuropathy (use pyridoxine if DM, renal failure, alcoholic, HIV, signs neuropathy)
Pyrazinamide (bactericidal); SE: hepatotoxic
Ethambutol (bacteriostatic); SE: optic neuritis