TB Flashcards
What pathogen is responsible for TB?
Mycobacterium tuberculosis (can be dormant beforehand)
How is TB transmitted?
Droplet-droplet/direct contamination
What is the aetiology of TB?
- Begins in terminal air spaces, bacteria engulfed by alveolar macrophages (not destroyed).
- Proliferate inside macrophage (cell death, bacteria released).
- Spreads via blood (usually asymptomatic).
- Macrophages activate CD4+ Th cells via MHC II, interferon gamma activates more macrophages.
- Aggregate around mycobacterium, granuloma forms.
- Caseous necrosis in centre of lesion to kill mycobacterium.
- Eventually sealed off by fibrous scar which can calcify, some bacteria can survive in dormant form and reactivate.
What are the risk factors for the reactivation of TB?
Children <5yrs, elderly, new TB infection, HIV, organ transplant, immunosuppression, IVDU, malnutrition, homeless, prison, poor.
What is unique about mycobacterium compared to other pathogens?
- Slow cell division (20hrs)
- Thick cell wall
- Resists decolourisation by acid (acid-fast)
What are the types of staining for acid-fast organisms?
- Ziehl-Neelsen
2. Auramine staining
What is this a presentation of?
Immigrant, HIV, immunosuppressed, elderly. 2-3 weeks cough (dry then productive), low grade fever, anorexia, weight loss, malaise, night sweats, sometimes haemoptysis.
TB
What are the investigations for suspected TB?
- CXR - upper lobe infiltrates and opacity, cavitation, calcification, effusion, lymphadenopathy, miliary TB (1-3mm nodules).
- Sputum acid-fast bacilli smear - 3 specimens including early morning sample.
- Sputum culture - precise identification and drug susceptibility.
- Nucleic acid amplification test - PCR, rapid diagnosis, detects drug resistance
- Diagnosis may be made on clinical findings and radiography.
- HIV test within 2 months
What is the management for active TB?
- Notify PHE
- 2 months intensive RIPE - rifampicin, isoniazid, pyrazinamide, ethambutol
- 4 months continuation - rifampicin, isoniazid
- Infectious until 3 AFB results negative, 2 weeks treatment, clinical improvement.
What is the management for contacts of latent TB?
- Testing for close contacts in last 2 years. BCG vaccine for Mantoux -ve contacts.
- Mantoux test - delayed type IV hypersensitivity, if +ve assess for active TB.
- Interferon gamma release assays (IGRA) - if had the BCG vaccine
What is the management for latent TB?
- If 35-65yrs with no hepatotoxicity, long term steroids, chemo, anti-TNFa.
- 3 months - rifampicin, isoniazid, pyridoxine
What are the side effects of rifampicin?
Body secretion coloured orange-red, hepatitis, rash, GI upset.
What are the side effects of isoniazid?
Peripheral neuropathy, hepatitis (give vitamin B6), rash.
What are the side effects of pyrazinamide?
Hyperuricaemia, hepatitis, rash, N&V, arthralgia, facial flushing.
What are the side effects of ethambutol?
Decrease in visual acuity, red green colour blindness (monthly vision checks if on for >2 months)
