Viral Pneumonia

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

Definition

Viral pneumonia is an infection of the lung tissue caused by viral pathogens, leading to inflammation and impaired gas exchange. It is more common in young children, older adults, and immunocompromised individuals.

Aetiology

Common viral causes include:

  • Influenza virus: the most common cause in adults.
  • Respiratory Syncytial Virus (RSV): common in infants and young children.
  • Adenovirus: can cause severe pneumonia in military recruits and immunocompromised patients.
  • Human metapneumovirus: affects young children and the elderly.
  • Parainfluenza virus: associated with croup and pneumonia in young children.
  • Coronavirus: includes SARS-CoV-2, which can cause severe viral pneumonia.
  • Varicella-zoster virus (VZV): can cause pneumonia in adults with chickenpox.

Pathophysiology

Viral pneumonia leads to:

  • Direct infection of lung epithelial cells, causing inflammation.
  • Increased mucus production and airway oedema.
  • Alveolar damage leading to impaired oxygen exchange.
  • Possible secondary bacterial infection.

Risk factors

  • Young children and older adults.
  • Chronic lung disease (e.g., COPD, asthma).
  • Immunosuppression (e.g., HIV, chemotherapy).
  • Smoking.
  • Recent viral illness.
  • Pregnancy (higher risk with influenza).

Signs and symptoms

Symptoms:

  • Gradual onset of dry cough.
  • Low-grade fever (may be high in influenza or COVID-19).
  • Breathlessness.
  • Fatigue and muscle aches.
  • Wheezing (more common in RSV and metapneumovirus).

Signs:

  • Tachypnoea (increased respiratory rate).
  • Reduced air entry on auscultation.
  • Fine inspiratory crackles.
  • Hypoxia in severe cases.

Investigations

  • Chest X-ray:
    • Shows bilateral interstitial infiltrates (diffuse patchy opacities).
    • Less likely to show lobar consolidation (seen in bacterial pneumonia).
  • Viral PCR testing:
    • Nasal or throat swab for influenza, RSV, COVID-19, or other suspected viruses.
  • Full blood count (FBC):
    • Usually normal or mildly raised white cell count.
    • Lymphocytosis may be seen in viral infections.
  • C-reactive protein (CRP):
    • Usually mildly elevated.
    • Markedly raised CRP (>100) suggests bacterial infection.
  • Oxygen saturation:
    • Assess need for oxygen therapy.

Management

1. Supportive Care:

  • Oxygen therapy: if SpO₂ <92%.
  • Fluids: IV fluids if dehydration is present.
  • Antipyretics: paracetamol for fever and discomfort.
  • Rest and symptom monitoring.

2. Antiviral Therapy (if indicated):

  • Influenza: antiviral therapy (if within 48 hours of symptom onset in high-risk groups).
  • COVID-19: Consider antiviral treatments in hospitalised or high-risk patients.
  • Varicella pneumonia: IV acyclovir if severe.

3. Antibiotics (only if secondary bacterial infection suspected):

  • if bacterial superinfection is suspected, start empirical antibiotics (e.g., co-amoxiclav or doxycycline).

Referral

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

  • Severe respiratory distress.
  • SpO₂ persistently <92% despite oxygen.
  • Haemodynamic instability (hypotension, tachycardia).
  • Confusion or altered mental status.
  • Severe immunosuppression (e.g., HIV, chemotherapy patients).
  • Failure to improve with outpatient treatment.
 
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