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Complications

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

Influenza causes up to 4000 deaths per year in the UK. The risk of complications of influenza is high in the following groups of patients:

  • people of all ages with chronic respiratory disease including asthma, chronic heart disease, chronic renal disease, chronic liver disease
  • with conditions and treatments that suppress the immune function
  • diabetes mellitus
  • all those aged 65 years or older
  • those in long stay residential care (1).

Complications include:

  • respiratory
    • acute bronchitis
      • most common lower respiratory tract complication and is seen in around 20% of influenza cases (2)
      • more common in elderly and those with medical conditions
    • influenza related pneumonia – the incidence varies widely (from 2% to 38%), generally seen frequently and with greater severity in patients with pre existing chronic cardiac and respiratory conditions
      • secondary bacterial pneumonia
        • more common
        • typically occurs four to five days after onset of illness
        • implicated pathogens include – Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenza Groups A, C and G beta-haemolytic streptococci
      • primary viral pneumonia
        • uncommon
        • typically become breathless within the first 48 hours of onset of fever
        • mortality in hospitalised patients is high (>40%) despite maximum supportive treatment on intensive care
    • exacerbations of chronic lung diseases such as asthma and COPD
      • up to 28% of exacerbations of COPD are associated with influenza A or B (2)
    • lung abscess, emphysema and invasive pulmonary aspergillosis (2)
  • cardiovascular
    • exacerbation of heart failure
    • ECG abnormalities – common, but most are not associated with cardiac symptoms
    • myocarditis – rare (1)
  • CNS
    • encephalitis/encephalopathy – rare, occurs within first week of illness, more common in children and Japan
    • Guillain-Barre syndrome
  • other complications
    • toxic shock syndrome
    • otitis media (in children) (3)
    • diabetic complications
    • myositis – occurs mostly in children infected with influenza B

Reference:

  1. British Infection Society; British Thoracic Society; Health Protection Agency. Pandemic flu: clinical management of patients with an influenza-like illness during an influenza pandemic. Provisional guidelines from the British Infection Society, British Thoracic Society, and Health Protection Agency in collaboration with the Department of Health. Thorax. 2007;62 Suppl 1:1-46.
  2. Turner D et al. Systematic review and economic decision modelling for the prevention and treatment of influenza A and B. Health Technol Assess. 2003;7(35):1-170
  3. Immunisation Against Infectious Disease - "The Green Book". Chapter 19. Influenza (October 2020)

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