Respiratory infections Flashcards
(53 cards)
Where is TB most common?
india, indonesia, pakistan, china, philippines
What organisms cause TB?
mycobacterium tuberculosis is most common, M. Bovis is also seen in cattle and some human, M. africanum is also seen in Africa.
What typeof bacteria is mycobacterium tuberculosis?
non motile rod shaped obliguate aerobe
What is M. tuberculosis cell wall made of and what implications does this have?
Long chain fatty acids
- staining characteristics (no gram stain)
- structural integrity
- withstand harsh envrionments
How quickly does M. tuberculosis divide?
every 15-20 hrs
How is TB spread?
Respiratory droplets released when coughing, sneezing and speaking. The infectious dose is only 1-10 bacteria but you need prolonged close contact exposure- at least 8 hrs a day for 6 months.
Describe the pathogenesis of TB
- inhaled infectious droplets
- engulfed by alveolar macrophages
- taken to local lymph nodes
- forms a primary complex
- 5% progress to active primary disease (if very virulent or immunocompromised)
- most go on to develop latent infection which heals/ self cures (95%) or is reactivated when the pt later becomes immunocompromised to cause post- primary active TB (5%)
What cell is responsible for handling primary TB infections?
T cells- as it is cell mediated immunity
Whats the difference between having a TB infection and having TB disease?
TB disease is when you get symptoms
How can you differentiate between TB infection and TB disease? (3)
If TB disease:
- symptomatic
- abnormal CXR
- sputum samples and cultures may be positive
Post primary TB disease may be due to exogenous reinfection or reactivation of latent TB. What may reactivate the TB?
- HIV
- substance abuse
- steroid treatment/ immunosurpression
- organ transplant
- haematological malignancy
- kidney disease
- diabetes
What are the most common extra pulmonary sites for TB disease to manifest? when do these most commonly occur?
- larynx
- lymph nodes
- pleura
- brain
- kidneys
- bones and joints
HIV or immunosurpressed pts
What is millary TB?
TB spreads through blood and is taken to all parts of the body. It is very rare.
What is a gohn focus?
the site of primary infection of TB
What are the risk factors for TB?
HIV, non UK born, immunocompromised, homeless, drug users, prisoners, close contacts, young adults and elderly
What signs and symptoms of TB are created by chronic T cell stimulation?
- fever (via TNFa, Il-6 and Il-1)
- night sweats
- weight loss and anorexia
- tiredness and malaise
What signs and symptoms does the active TB directly cause?
- cough
- sometimes haemoptysis
- breathlessness if pleural effusion
- consolidation
- cavitation and fibrosis
How should TB be investigated? Describe what should/ may be found?
- CXR- find patchy consolidation +/- cavitation, usually upper lobes/ apices
- Biposy- not often done but caseous necorsis indicates TB
- Sputum samples
- Tuberculin skin testing (mantoux test)- will be positive if they have every had/ have TB infection
- Interferon gamma releasing assays- detects INF-y specific to TB, so will be positive if theyve ever had/ ahve TB
How can sputum samples be used to diagnose TB?
- need 3 samples, with one positive
- smears are stained with zeihl neelson stain or auramine (fluorescent)
- need culturing so can take upto 3 weeks
- NAAT can also be used for quicker diagnosis and check for drug resistance mutations
How is TB treated?
RIPE: - Rifampicin (6 months) - Isoniazid (6 months) - Pyrazinamide (2 months) - Ethambutol (2 months) sometimes also streptomycin Surgery can sometimes be done if just one lobe affected
What are the 2 main side effects of TB drugs?
rifampicin turns wee orange
theyre all hepato and probably nephrotoxic
Why are so many drugs needed to treat TB?
- stop resistance forming
- long term because it multiplies so slowly
What are the diadvantages of the mantoux test?
- prone to false positives if BCG vaccinated
- also false negatives if HIV or immunosurpressed
- also cannot differentiate between latent and active disease
How effective is the BCG vaccine?
70% effective in children, less effective in adults
