🎯 Pathology

• self-limiting viral infection that affects the upper respiratory tract

• can be life-threatening in the elderly, pregnant women and in the immunocompromised

• spread from person-to-person via inhaled droplets

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💡Causes

• there are 4 types of influenza viruses: A, B, C and D

  • only A and B cause infection in humans

• influenza A

  • combination of hemagglutinins (H) and neuraminidase (N) proteins on the surface determine the subtype

  • there are 18 subtypes of H, and 11 subtypes of N

    • e.g. H1N1, H3N2

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🩺 Clinical features

• fever

• cough

• sore throat

• coryzal symptoms

• myalgia

• malaise

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🕵️‍♂️ Investigations

• clinical especially during influenza season

• methods of testing:

  • viral PCR - high sensitivity specificity, and results are available within 1 to 8 hours

  • rapid antigen testing - results available within 15 minutes

  • viral culture - high sensitivity and specificity but results take several days

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💆‍♂️ Management

• self-limiting in healthy individuals

• neuraminidase inhibitors (antivirals) e.g. oseltamivir as early as possible (within 48 hours) for:

  • severe illness

  • patients at risk of complications

    • chronic disease

    • immunocompromised

    • pregnancy

    • over 65 years of age

    • younger than 6 months of age

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Prevention

• neuraminidase inhibitors may be used to prevent influenza infection

• annual influenza vaccination at the start of the winter season

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Seasonal versus pandemic influenza

• seasonal influenza

  • antigenic drift: small genetic changes occur during viral replication

  • this is what the annual vaccine targets

• pandemic influenza

  • antigenic shift: new H and N combinations are made

  • no immunity in the population