Influenza

“Acute respiratory tract infection that is typically seasonal in nature with local community outbreaks, epidemics, and, rarely, pandemics“

Risk Factors

• Winter season
• Known current influenza outbreak
• Unvaccinated against influenza
• Healthcare workers

Aetiology

• Influenza A virus – frequently causes outbreaks & more virulent
• Influenza B virus – co-circulates with influenza A & less severe clinical illness
• Influenza C virus – mild or asymptomatic infection

Pathophysiology

1. Transmitted through infected respiratory droplets aerosolised by coughing and sneezing
2. The virus binds to and enters tracheobronchial ciliated epithelium using its viral surface haemagglutinin (H antigen)
3. Viral replication occurs with peak viral shedding (aided by neuraminidase [N antigen]) occurring within 48-72 hours of exposure

Clinical Presentation

• Coryza
• Nasal discharge
• Fever
• Cough
• GI symptoms
• Headache
• Malaise
• Myalgia
• Arthralgia
• Conjunctivitis
• Sore throat

Investigations

• Diagnosis is typically clinical when it is known to be circulating in the community, laboratory testing for at-risk groups, rapid testing available in hospitals

Management

• Conservative:
  • Adequate hydration
  • Paracetamol/Ibuprofen
  • Rest
  • Anti-viral treatment for at-risk groups (oseltamivir/zanamivir)
  • Urgent admission to hospital if the infection is complicated by sequalae or concomitant disease
• Annual vaccination for at-risk groups

Complications

• Acute bronchitis
• Pneumonia (bacterial or viral)
• Exacerbations of asthma or COPD
• Otitis media
• Sinusitis