Respiratory Infections - Bacteria

Question 1

Describe some methods of respiratory bacterial infection.

Answer 1

• Respiratory droplets released by coughing/sneezing
• Occur by touching object/surfaceexposed to bacteria

Question 2

Give some examples of upper respiratory tract infections.

Answer 2

• Rhinitis - common cold
• Adenoiditis - children mainly
• Pharyngitis (=tonsilitis)
• Sinusitis
• In these cases, fever, headache, coughing, sweats, pain and purulent discharge may be present

Question 3

Give examples of lower respiratory tract infections.

Answer 3

• Epiglottitis - compromised airflow
• Laryngitis - croup may occur if infection extends below larynx - stridor (whistling)
• Bronchitis - phlegm production, SOB, tachypnoea (rapid breathing)
• Pneumonia and pleurisy

Question 4

Describe the normal microbiota of the respiratory tract.

Answer 4

• Warm, moist environment - commensals in upper respiratory tract
• Lower respiratory tract, sinus and middle ear usually sterile

Question 5

What are the main defences against respiratory tract infections?

Answer 5

• Mucociliary escalator - to trap microbes
• SIgA and macrophages in bronchioles/alveoli

Question 6

Describe epiglottitis

Answer 6

• Caused by Haemophilus influenzae
• Some strains produce capsule
• Children aged 4-6 years most at risk
• Vaccine - highly effective

Question 7

Describe Strep throat infections

Answer 7

• Common in children
• Present with high fever and red, swollen tonsils
• Can progress to scarlet fever, sepsis, rheumatic fever
• Penicillin and erythromycin usually used

Question 8

Describe diphtheria

Answer 8

• Caused by Corynebacterium diphtheriae - Gram positive bacillus
• Toxic strains can occur e.g AB toxin
• Antitoxin prevents entry into cell
• DTP vaccine is available
• Cases rare due to herd immunity

Question 9

Describe hospital acquired pneumonia.

Answer 9

• Develops at least 48 hours following hospital admission
• Includes postoperative pneumonia
• Does not include patients with ventilator-associated pneumonia

Question 10

Describe common characteristics of lower respiratory tract infections.

Answer 10

• COMMON PRESENTATION - Dyspnoea, productive cough, fever and raised inflammatory markers
• Common examples are acute bronchitis, acute exacerbations of chronic bronchitis, community acquired pneumonia
• Acute bronchitis - infection of large airways - tracheobronchial tree - mainly due to viruses

Question 11

How does acute exacerbation of chronic bronchitis occur?

Answer 11

• Sudden worsening of COPD symptoms
• Increased purulence of sputum
• Usually viral

Question 12

Describe pneumonia.

Answer 12

• Infection of lung tissue, alveoli and terminal bronchioles
• Classified based on anatomical distribution
• Higher incidence in patients who are asplenic, immunocompromised, diabetic or alcoholic

Question 13

What accounts for 40% of community acquired pneumonia?

Answer 13

Streptococcus pneumoniae

Question 14

Describe Staph. aureus

Answer 14

• May cause clinically acquired infection in those with risk factors e.g HIV/influenza infection
• Less common than bacterial causes, viruses such as influenza virus - can also cause viral pneumonia

Question 15

Describe Strep. pneumoniae. PART 1

Answer 15

• Pneumococcus - coloniser of upper respiratory tract
• Invasion into lower respiratory tract requires reduced host defences/increased bacterial evasion of host immune system

Question 16

Describe Strep. pneumoniae. PART 2

Answer 16

• Pathogens have virulence factors - enhance survival in respiratory epithelium
• EXAMPLE - Pneumococcus - gene encoding polysaccharide capsule

Question 17

What is the function of the polysaccharide capsule in Pneumococcus and what does it allow Pneumococcus to do?

Answer 17

• Capsule helps bacteria evade phagocytosis - inhibits complement cascade of innate immune system. Prevents mucosal clearance by cilia
• Once in lower respiratory tract, inflammation and damage to mucosa causes fluid accumulation in alveoli. Reduced surface for respiration and hypoxia

Question 18

What does the fluid accumulation in the alveoli appear as on a CXR?

Answer 18

Consolidation

Question 19

How can bacterial respiratory tract infections be diagnosed and treated?

Answer 19

• Blood and sputum cultures
• Molecular testing
• Penicillin - treatment of choice for Strep. pneumoniae.
• Macrolides instead for penicillin-allergic patients