Bacterial Pneumonia

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management | Referral

Definition

Bacterial pneumonia is an infection of the lung parenchyma caused by bacteria, leading to alveolar inflammation, consolidation, and impaired gas exchange.

Aetiology

Common bacterial causes include:

  • Streptococcus pneumoniae – most common cause of community acquired pneumonia (CAP).
  • Haemophilus influenzae – more common in COPD patients.
  • Staphylococcus aureus – seen in post-viral pneumonia.
  • Moraxella catarrhalis – more common in immunocompromised individuals.
  • Atypical bacteria:
    • Mycoplasma pneumoniae – common in younger adults.
    • Legionella pneumophila – associated with outbreaks and contaminated water sources.
    • Chlamydophila pneumoniae – mild, often self-limiting.

Pathophysiology

Bacterial pneumonia occurs when bacteria enter the lower respiratory tract, leading to:

  • Alveolar infiltration by inflammatory cells.
  • Capillary leak and exudate formation.
  • Alveolar consolidation, impairing gas exchange.
  • Potential complications, including pleural effusion and sepsis.

Risk factors

  • Age >65 or <5 years.
  • Chronic lung conditions (e.g., COPD, asthma).
  • Smoking and alcohol misuse.
  • Immunosuppression (e.g., chemotherapy, HIV).
  • Recent viral upper respiratory infection.
  • Hospitalisation or recent antibiotic use.

Signs and symptoms

Symptoms:

  • Sudden onset fever and chills.
  • Productive cough with purulent or rusty sputum.
  • Pleuritic chest pain (worse with deep breathing).
  • Breathlessness.
  • Fatigue and malaise.

Signs:

  • Pyrexia (fever).
  • Tachypnoea (increased respiratory rate).
  • Reduced breath sounds on auscultation.
  • Bronchial breathing over affected lobes.
  • Dullness to percussion.
  • Increased vocal resonance.

Investigations

  • Chest X-ray:
    • Shows lobar or patchy consolidation.
    • Can detect complications like pleural effusion.
    • X-ray of lobar pneumonia

    Figure: Chest X-ray showing lobar pneumonia affecting the right middle lobe.
    Source: Häggström, M. (2018).

  • Blood tests:
    • Raised white cell count (WCC) suggests bacterial infection.
    • Raised CRP (>100 mg/L suggests significant infection).
  • Sputum culture: identifies causative bacteria.
  • Oxygen saturation: assess severity and need for oxygen therapy.
  • Blood cultures: if sepsis is suspected.

Management

1. Antibiotic Therapy:

  • Community-acquired pneumonia (CAP):
    • First-line: Amoxicillin 500 mg TDS for 5 days.
    • Alternative (penicillin allergy): Doxycycline 200 mg stat, then 100 mg OD.
  • Hospital-acquired pneumonia (HAP) (onset >48 hours post-admission):
    • First-line: Co-amoxiclav 625 mg TDS for 7 days.
    • Severe cases: Piperacillin/tazobactam IV or follow local guideline.

2. Supportive Care:

  • Oxygen therapy: if SpO₂ <92%.
  • Analgesia: paracetamol for fever and pain relief.
  • Hydration: encourage fluids, IV if needed.

3. Escalation if Severe:

  • Consider high-dependency or ICU referral for respiratory failure.
  • Non-invasive ventilation (e.g., CPAP) if significant hypoxia.

Referral

Refer to secondary care if any of the following are present:

  • CURB-65 score ≥2: increased risk of severe pneumonia.
  • Respiratory distress: severe tachypnoea or hypoxia.
  • Haemodynamic instability: hypotension, confusion.
  • Failure of outpatient treatment: persistent fever or worsening symptoms.
 
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