Influenza virus

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
  • Oseltamivir
  • Zanamavir
  • Peramivir is IV only
• 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