Respiratory System >
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
- Transmitted through infected respiratory droplets aerosolised by coughing and sneezing
- The virus binds to and enters tracheobronchial ciliated epithelium using its viral surface haemagglutinin (H antigen)
- 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