Influenza virus

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Background

Microbiology

  • Enveloped, single-stranded, negative-sense RNA virus in the Orthomyxoviridae family
  • Four genera corresponding to influenza A through D
  • Typed by hemagglutinin (HA) and neuraminidase (NA) proteins
    • Antigenic drift refers to small mutations
    • Antigenic shift refers to large changes from reassortment

Epidemiology

  • Worldwide
  • Seasonal in temperate climates, lasting from fall through spring and peaking in late winter
  • Antigenic drift usually results in local outbreaks, while antigenic shift can result in epidemic or pandemics

Clinical Manifestations

  • Fever and respiratory symptoms, especially with myalgias

Management

  • Neuraminidase inhibitors started within 48 hours of symptom onset are associated with a shorter duration of illness
  • Monitor for secondary bacterial pneumonia

Prevention

  • Annual influenza vaccination is recommended for everyone 6 months of age and older
  • Chemoprophylaxis with oseltamivir may be indicated as post-exposure prophylaxis or during local outbreaks for all people at risk