What are the 3 most common bacteria associated with human TB??
Mycobacterium tuberculosis
Mycobacterium bovids
Mycobacterium africanum
Describe some features of mycobacterium tuberculosis
Non-motile
Rod-shaped
Obligate aerobe
Has a very thick layer of fatty acids, glycolipids etc
Need Acid-Fast stain (cannot stain with Gram stain)
Why does mycobacterium TB take a long time to culture?
Relatively slow growing bacteria
Generation time 15-20 hours
Takes a minimum of 2 weeks to culture
How is TB spread?
Respiratory droplets (coughing/sneezing) Infectious dose is very low Air remains infectious for 30 minutes
Is it easy to catch TB?
No
Usually need prolonged exposure to catch it
What are the classic situations in which TB spreads?
Overcrowding situations:
Poor housing
Prisons
Homeless people
Describe the pathogenesis of TB
Inhaled aerosols/droplets
Engulfed by alveolar macrophages
Drainage of lung to local lymph nodes
Primary complex/focus of infection established
Progression to primary active disease or initial containment of infection to latent
What are the 2 outcomes of latent infection?
Heals/self cure
Reactivation of post-primary TB
What is the commonest type of TB?
Reactivation of latent to post-primary TB
Describe how tests for latent TB would appear
TST (mantoux) and IFN gamma tests would be positive
Chest x-ray normal
Sputum smears and cultures normal
Asymptomatic
What are the main symptoms of active TB
Cough
Fever
Weight loss
What is miliary TB?
TB disseminated wide into the body via the blood stream
(Tiny spots throughout lung fields on x-ray)
Rare
What are some of the risk factors for reactivation?
HIV Substance abuse Prolonged corticosteroid therapy Immunosuppressants TNF alpha antagonist Low body weight Organ transplant Haematological malignancy Severe kidney disease Diabetes mellitus Silicosis
What are caseating granulomata in TB?
Lung parenchyma and lymph nodes
Liquified and cheesy looking material
Dead and dying bacilli and inflammatory cells
Langhan’s giant cells present
What are the common sites for extrapulmonary TB?
Larynx Lymph nodes Kidneys Pleura Brain Bones and joints
What are some risk factors for TB
Non-Uk born/recent migrants HIV infected Immunocompromised Homeless Drug users Prisoners Close contacts of patients with TB Young adults
What Hx would suggest TB?
Recent arrival/travel Contacts with TB BCG vaccination? Fever Weight loss Malissa Anorexia
List some symptoms of pulmonary TB
Fever Night sweats Weight loss/anorexia Tiredness Malaise Cough Haemoptysis Breathlessness
What are some signs on examination of pulmonary TB?
Fever Often no chest signs CXR abnormality May be crackles in infected areas (Pleural involvement = dullness)
What investigations would you run for TB??
CXR
Sputum - 3 early morning samples
Induced sputum via physiotherapy
Bronchoscopy
What would you see on a CXR for TB?
Apex of the lung often involved
Ill defined patchy consolidation
Cavities can develop in consolidation
Healing results in fibrosis
Why are sputum smears not very good in diagnosing TB?
Not very sensitive
May only have a few bacilli in
Operator dependents
What is the gold standard investigation for diagnosis of TB?
Culture (but takes approximately 2 weeks)
What are epitheloid cells?
Activated macrophages
Can fuse together to form giant cells
Describe the tuberculin sensitivity test (TST)/mantoux
Look for latent TB
Challenge with an antigen previously exposed to
Infected intra-dermally
Inflammation, red circle appear at injection site
Read 2-3 days later
(Can get false positives and false negatives)
Describe interferon gamma releasing assays (IGRAs)
Buffer test for latent TB
Blood test
No cross reaction with BCG
Cannot distinguish between latent and active TB
What is the first line medication for TB?
4 first line medications: Rifampicin Isoniazid Pyrazinamide Ethambutol
What are some problems with Rifampicin?
Can give orange secretions (tears/urine)
Cannot take whilst on the contraceptive pill
What is the bad side effect of ethambutol?
Can cause visual disturbance
What are the second line drugs for TB?
Quinolones
Clofazamine
PAS
Ethionamide
Why do we always use a combination of drugs to treat TB?
TB is notorious for producing mutations
Don’t want to select for a particular strain
What is the minimum course of treatment for TB?
6 months
What is scrofula?
A lymphadenitis
Disease with glandular swellings
Probably a form of TB
Give some common clinical signs of extrapulmonary TB
Lymphadenitis
Ascites
Adhesions of peritoneum
Pott’s disease
What is Pott’s disease?
A form of TB where disease is seen in the vertebrae
Name some of the TB prevention methods
All forms of TB must be notified to public health
Personal protective equipment
Negative pressure isolation
Susceptible people vaccinated
Describe BCG vaccine
Live vaccine
From mycobacterium bovis strain
Given to babies in high prevalence communities
70-80% effective
What is asthma?
Chronic inflammatory disorder of the airways
Reversible airway obstruction caused by inflammation, bronchoconstriction and mucus
Describe what happens during an asthma attack
Environmental trigger breathed in
Inflammation driven by TH2 cells
Type 1 hypersensitivity reaction (immediate)
Airway narrowing - SM contraction, mucus production and inflammatory cell infiltration
Is asthma restrictive or obstructive?
Obstructive
What would the FEV1/FVC look like in asthma?
Before treatment = FEV1 reduced, FVC normal
After treatment = FEv1 and FVC normal
Why is it difficult to diagnose asthma?
There is no standardisation of type, severity, frequency, symptoms or investigation findings
(Everybody gets it differently)
What are the reversible symptoms of asthma?
Wheeze
Breathlessness
Chest tightness
Cough
What is a wheeze?
High pitched
Expiratory musical sound
From narrowed airways
Describe the typical features of a cough due to asthma
Worse at night
Dry
Exercise induced
Non-productive
Give some clinical signs of asthma
Respiratory rate increase Tracheal tug Recession Nasal flaring Accessory muscle use
Give some features of a typical Hx for asthma
Eczema, hay fever etc (atopy)
Smoker/smoking in home
Mould in home/live on farm/pets
Describe the peak flow of an asthmatic patient
Varies over the day
Diurnal variation
Treatment stabilises this a lot
Should increase after inhaler use
What do we measure with spirometry?
FEV1
FVC
What do we do first for someone with suspected asthma?
Trial them on bronchodilators for 1 month then review
See if symptoms and peak flow gets better
Give some prevention methods for asthma
Change pillows and bedsheets every few years
Fresh air
Stop smoking
What is the approach to asthma treatment?
Step up, step down
Step up to other medications if getting worse or down to less if getting better
What is the general progression of treatment for an asthmatic getting worse?
Short acting inhalers
+ steroid inhalers
Long acting inhalers
Specialist care
How does a short acting beta agonist work?
Helps to relax smooth muscle
Quick relief
When do people require a step up from short acting inhalers?
If using the inhaler more than 3 times a week
Or if nocturnal symptoms occur more than once a week
How to steroid inhalers work?
Preventer
Reduces inflammation - inhibitors of inflammatory cells and mediators
Prevents attacks
Describe the clinical features of a mild asthma attack
Sats >92% Pulse <110 Resp rate <25 Speech normal Minimal wheeze PEFR >75% predicted
Describe the clinical features of a moderate asthma attack
Sats >92% Pulse <110 Resp rate <25 Speech normal wheeze +++ PEFR 50-75% predicted
Describe the clinical features of a severe asthma attack
Sats <92% Pulse >110 Resp rate >25 Can't complete sentences No wheeze PEFR 35-50% predicted
How do you treat a severe asthma attack?
Give lots of salbutamol via a nebuliser
With a continuous stream of oxygen
Describe the clinical features of a life threatening asthma attack
Sats <92% (cyanosis) Silent chest/poor expiratory effort Altered consciousness Exhaustion PEFR 35% predicted
Why do we sometimes need to give IV salbutamol?
Sometimes the mediation struggles to get through the thick layer of mucus when in an inhaler
What is the treatment for a life threatening asthma attack?
Do the A-E assessment
Be aware they may go into cardiac arrest
Oxygen
Salbutamol nebulisers - back to back until airways open
IV access (need to cannulate ASAP) - salbutamol