Bacterial Pneumonia

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management | Patient Advice

Definition

Bacterial Pneumonia is an infection of the lung parenchyma caused by bacterial pathogens, leading to inflammation and consolidation. It is characterised by symptoms such as cough, fever, and difficulty breathing.

Aetiology

The most common bacterial causes of pneumonia include:

• Streptococcus pneumoniae: The leading cause of community-acquired pneumonia (CAP).
• Haemophilus influenzae: Common in patients with underlying lung conditions.
• Staphylococcus aureus: More common after influenza infection.
• Klebsiella pneumoniae: Associated with alcohol misuse or aspiration.
• Atypical Pathogens: Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella pneumophila.

Pathophysiology

Bacterial pneumonia occurs due to the invasion of bacterial pathogens into the alveoli, leading to:

• Inflammation: Recruitment of immune cells causes alveolar oedema and exudate formation.
• Consolidation: Replacement of air in the alveoli with inflammatory exudate impairs gas exchange.
• Systemic Effects: Release of inflammatory mediators can lead to fever and malaise.

Risk Factors

Factors that increase the risk of bacterial pneumonia include:

• Smoking or exposure to second-hand smoke.
• Underlying chronic lung disease (e.g., COPD, asthma).
• Immunosuppression (e.g., HIV, cancer treatment).
• Age (very young or elderly).
• Recent viral respiratory infections (e.g., influenza).
• Alcohol misuse or malnutrition.

Signs and Symptoms

Common clinical features of bacterial pneumonia include:

• Cough: Productive with purulent or blood-streaked sputum.
• Fever and Chills: Often with acute onset.
• Dyspnoea: Shortness of breath, particularly with exertion.
• Pleuritic Chest Pain: Sharp pain worsening with deep breaths or coughing.
• Tachypnoea: Rapid breathing.
• Fatigue and Malaise: Generalised tiredness.

Investigations

Diagnostic tests and findings include:

• Clinical Examination:
  • Decreased breath sounds or crackles on auscultation.
  • Dullness to percussion over the affected area.
• Chest X-ray: Shows lobar or patchy consolidation.
• Blood Tests:
  • Full Blood Count: Elevated white cell count (leukocytosis).
  • C-reactive Protein (CRP): Raised, indicating inflammation.
• Sputum Culture: To identify causative bacteria and guide antibiotic therapy.
• Blood Cultures: Recommended in severe cases to detect bacteraemia.
• Pulmonary Function Tests: Not routinely required but may aid in assessing respiratory impairment.

Management

1. Outpatient Management

• Empirical Antibiotics:
  • First-line: Amoxicillin 500 mg TDS for 5–7 days.
  • Alternative (penicillin allergy): Doxycycline 200 mg on day 1, then 100 mg OD.
• Symptomatic Relief: Paracetamol or ibuprofen for fever and pain.
• Hydration: Encourage fluid intake.

2. Hospital Management (Moderate to Severe Cases)

• Oxygen Therapy: To maintain SpO₂ > 92%.
• Intravenous Antibiotics:
  • Co-amoxiclav.
  • Clarithromycin for atypical coverage.
• Fluid Management: Intravenous fluids for dehydration or septic shock.
• Chest Physiotherapy: To aid mucus clearance in selected cases.
• Intensive Care Referral: For respiratory failure or severe sepsis.

Patient Advice

Key advice includes:

• Complete the full course of antibiotics, even if symptoms improve.
• Maintain adequate hydration and rest during recovery.
• Avoid smoking or exposure to smoke to aid lung recovery.
• Seek medical attention if symptoms worsen, such as increased breathlessness or fever.
• Ensure vaccinations are up-to-date, including pneumococcal and annual influenza vaccines.