Session 9 - Tuberculosis, Lower Respiratory tract infection, & Pneumonia Flashcards
(30 cards)
Which bacterium causes tuberculosis?
Mycobacterium Tuberculosis (most commonly)
- M bovis
- M africanum (certain cases from Africa)
Describe the microbiology of Mycobacterium Tuberculosis.
- Non-motile rod-shaped bacteria.
- Obligate aerobe
- Long-chain fatty (mycolic) acids, complex waxes, and glycolipids in cell wall. (structural rigidity, can be stained)
- Relatively slow growing compared to other bacteria.
- Generation time 15-20h
How is M Tuberculosis spread?
By respiratory droplets, coughing and sneezing.
Suspended in the air.
Contagious but not easy to acquire infection, prolonged exposure fascilitates transmission. (at least 8 hours/day upto 6 months)
How does TB progress once the bacteria enter a host?
- Inhaled infectious droplets.
- Engulfed by alveolar macrophages.
- Local lymph nodes.
- Primary Complex
a) 5% progress to Active disease (primary)
b) Initial containment
5. Latent infection
(i) 95% heal/ self cure
(ii) Reactivation - Post Primary TB
What is the difference between Latent TB infection and TB Disease (in lungs)?
Latent TB
- Inactive (contained tubercle bacilli in body)
- TST or IFN gamma tests +ve
- Chest X-ray normal
- Sputum cultures normal
- No Symptoms
- Not infectious
- Not a case of TB
TB Disease
- Active, multiplying tubercle bacilli in body
- TST or blood test results usually positive
- Chest X-ray usually abnormal
- Sputum smears/ cultures may be +ve
- Often infectious before treatment.
- A CASE of TB!
Describe the characteristics of primary TB.
- Ghon focus/ complex (Primary lesion)
- Limited by cell mediated immunity
- Occasionally symptomatic (miliary/ disseminated)
How does Post-primary TB present?
- As pulmonary or extra-pulmonary.
What are the risk factors for reactivation of TB?
- HIV infection.
- Substance abuse.
- Prolonged therapy with corticosteroids or immunosuppression.
- TNF-a antagonists.
- Organ transplant.
- Haematological malignancy.
- Sever kidney disease (dialysis).
- Diabetes M.
- Silicosis.
What is extra-pulmonary TB?
TB infection in place other than lungs.
- Larynx
- Lymph nodes - most commonly cervical
- Pleura
- Brain
- Kidneys - slow progression, spread to lower Urinary tract.
- Bones/ Joints
Which group of people are more likely to get extra-pulmonary TB?
- HIV infected
- Immunosuppressed patient
- Young children
What is miliary TB?
TB carried through the blood stream to all parts of the body. (very rare)
Which people would TB be more suspected in (risk factor)?
- Non-UK born/ recent migrant
- HIV patient
- Homeless
- Drug user
- Close contact (prison)
- Younger adults (or elderly)
What are the symptoms of pulmonary TB?
- Fever
- Night sweats
- Weight loss + Anorexia
- Tiredness and malaise
- Cough (most common)
- Breathlessness + Pleural effusion
(may be crackles, or cavitation/ fibrosis in extensive disease)
Which investigations should be done for pulmonary TB?
- Chest X-Ray
- Sputum - 3 early morning samples
- Bronchoscopy
What is often seen on a CXR in TB?
- Apex of lung often involved
- Ill defined patchy consolidation
- Cavitation usually develops within consolidation
- Healing causes fibrosis
(pleural effusion often seen)
Which lab test confirms TB is the infective organism?
- Sputum culture is gold standard, up to 6 weeks of incubation.
- Microscopy of sputum can also be done, staining for the bacilli.
How do granuloma appear in TB in the lung? What type of necrosis is this?
Caseous Necrosis.
- Many immobile epithelioid histiocytes and lymphocytes surrounding a centre of caseous necrosis, usually in lung.
Which diagnostic test is used to test if a person has been exposed to TB?
Mantoux test (tuberculin sensitivity test) Under the skin, then the size of the area is measured 48-72 hours later.
What are the limitations of the mantoux test?
- False positives (BCG vaccine, non TB)
- False negatives (e.g. immunocompromised - HIV etc)
What are the first line drugs used to treat TB?
- Rifampicin (R)
- Isoniazid (H)
- Pyrazinamide (Z)
- Ethambutol (E)
For 2 months, then first 2 for 4 months.
(18 months if CNS TB)
How is TB managed?
- Early + adequate treatment with combination antibiotics (at least 6 months)
- Close monitoring of compliance.
This makes the patient Non-infectious and there are then no secondary transmission or cases.
Which factors increase drug resistance?
- Natural mutations in replication means there are small number of drug resistant organisms.
- Improper regimen of antibiotics or poor compliance leads to selection of the mutant bacteria.
- Now there is a single population of multi-drug resistant bacteria.
- Delays in diagnosis, overcrowding and inadequate infection control lead to facilitation of transmission of the drug resistance.
What treatment is given for multi-drug resistant and extremely drug resistant forms of TB?
If not responding to normal regimen:
- 4-5 Drug regimen - longer duration
- Quinolones, aminoglycosides, PAS, cyloserine, ethionamide.
Which organs are involved in miliary TB?
Often multiple organs (always lungs involved, with few resp symptoms).
Headache - meningeal
Pericardial/ pleural effusions (small)
- Ascites can be present.
- Retinal involvement (choroid tubercles seen)
