Pneumonia

Question 1

3 sources of respiratory infection?

Answer 1

1. Human-human transmission
2. Environment e.g. legionella through air conditioning systems
3. Animals e.g. psitaccosiis – pneumonia caught from birds

Question 2

How do respiratory bacteria cause pneumonia? (3)

Answer 2

• Colonise the nasopharynx or are inhaled into the alveolus
• Adhere to respiratory cells
• If they evade the immune system they multiply and express virulence factors, causing disease

Question 3

What are respiratory innate defences? (6)

Answer 3

• Mucus
• Ciliated cells
• Mucociliary clearance elevator
• Alveolar macrophages
• PMN leucocytes
• Complement

Question 4

What is mucociliary clearance elevator? (3)

Answer 4

• Particles are trapped in mucus covering respiratory tract
• Ciliary action drags the mucus upwards, so it can be coughed/spat (expectorated) out
• Disruption of this mechanism results in chronic infections – e.g. cystic fibrosis or bronchiectasis

Question 5

How does complement fight bacteria? (3)

Answer 5

• Bacterial cell wall components that enter the respiratory system activate the alternate complement pathway
• Complement then attracts PMNs and macrophages
• Complement opsonises bacteria

Question 6

How does phagocyte activation (PMNs and macrophages) fight bacteria? (2)

Answer 6

• Engulf bacteria
• Kill bacteria through lytic enzymes and reactive oxygen intermediates

Question 7

Community acquired pneumonia (CAP) (6)

Answer 7

• Definition: “Symptoms and signs consistent with an acute lower respiratory infection associated with new radiographic shadowing for which there is no other explanation”
• Most common fatal infection – 1-3 cases per 100, higher rate of infection in the elderly
• Mortality = 5-15% - high in elderly in developed countries and children in developing countries
• Complications – emphysema, lung abscess
• Common bacterial causes: extracellular – strep pneumonia (>50% - typical), haemophilus influenza (10% - secondary). Intracellular (atypical – primary) – mycoplasma pneumonia (10%), legionella pneumophila (2%), Chlamydia pneumonia and Chlamydia psitacci, coxiella burnetti.
• Tuberculosis also a common cause

Question 8

What causes pneumococcal infections?

Answer 8

• Streptococcus pneumoniae (S. pneumoniae) bacterium