Respiratory Infections - Bacteria Flashcards
Describe some methods of respiratory bacterial infection.
- Respiratory droplets released by coughing/sneezing
- Occur by touching object/surfaceexposed to bacteria
Give some examples of upper respiratory tract infections.
- Rhinitis - common cold
- Adenoiditis - children mainly
- Pharyngitis (=tonsilitis)
- Sinusitis
- In these cases, fever, headache, coughing, sweats, pain and purulent discharge may be present
Give examples of lower respiratory tract infections.
- Epiglottitis - compromised airflow
- Laryngitis - croup may occur if infection extends below larynx - stridor (whistling)
- Bronchitis - phlegm production, SOB, tachypnoea (rapid breathing)
- Pneumonia and pleurisy
Describe the normal microbiota of the respiratory tract.
- Warm, moist environment - commensals in upper respiratory tract
- Lower respiratory tract, sinus and middle ear usually sterile
What are the main defences against respiratory tract infections?
- Mucociliary escalator - to trap microbes
- SIgA and macrophages in bronchioles/alveoli
Describe epiglottitis
- Caused by Haemophilus influenzae
- Some strains produce capsule
- Children aged 4-6 years most at risk
- Vaccine - highly effective
Describe Strep throat infections
- Common in children
- Present with high fever and red, swollen tonsils
- Can progress to scarlet fever, sepsis, rheumatic fever
- Penicillin and erythromycin usually used
Describe diphtheria
- 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
Describe hospital acquired pneumonia.
- Develops at least 48 hours following hospital admission
- Includes postoperative pneumonia
- Does not include patients with ventilator-associated pneumonia
Describe common characteristics of lower respiratory tract infections.
- 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
How does acute exacerbation of chronic bronchitis occur?
- Sudden worsening of COPD symptoms
- Increased purulence of sputum
- Usually viral
Describe pneumonia.
- Infection of lung tissue, alveoli and terminal bronchioles
- Classified based on anatomical distribution
- Higher incidence in patients who are asplenic, immunocompromised, diabetic or alcoholic
What accounts for 40% of community acquired pneumonia?
Streptococcus pneumoniae
Describe Staph. aureus
- 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
Describe Strep. pneumoniae. PART 1
- Pneumococcus - coloniser of upper respiratory tract
- Invasion into lower respiratory tract requires reduced host defences/increased bacterial evasion of host immune system
Describe Strep. pneumoniae. PART 2
- Pathogens have virulence factors - enhance survival in respiratory epithelium
- EXAMPLE - Pneumococcus - gene encoding polysaccharide capsule
What is the function of the polysaccharide capsule in Pneumococcus and what does it allow Pneumococcus to do?
- 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
What does the fluid accumulation in the alveoli appear as on a CXR?
Consolidation
How can bacterial respiratory tract infections be diagnosed and treated?
- Blood and sputum cultures
- Molecular testing
- Penicillin - treatment of choice for Strep. pneumoniae.
- Macrolides instead for penicillin-allergic patients
