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  • image Influenza is a viral illness associated with high mortality and high hospitalization rates among persons older than age 65 years. The aging of the population is contributing to an increased disease burden in the United States.
  • image Seasonal influenza epidemics are the result of viral antigenic drift, which is why the influenza vaccine is changed on a yearly basis. Antigenic drift forms the foundation of the recommendation for annual influenza vaccination.
  • image The acquisition of a new hemagglutinin and/or neuraminidase by the influenza virus is called antigenic shift, which results in a novel influenza virus that has the potential to cause a pandemic.
  • image The primary route of influenza transmission is person-to-person via inhalation of respiratory droplets, and transmission can occur for as long as the infected person is shedding virus from the respiratory tract.
  • image Clinical diagnosis of influenza is difficult. Classic signs and symptoms include abrupt onset of fever, muscle pain, headache, malaise, nonproductive cough, sore throat, and rhinitis. These signs and symptoms usually resolve within 1 week of presentation.
  • image In the United States, the primary mechanism of influenza prevention is annual vaccination. Vaccination not only prevents influenza illness and influenza-related hospitalizations and deaths but also may decrease healthcare resource use and the overall cost to society.
  • image The trivalent influenza vaccine (TIV) and the live-attenuated influenza vaccine (LAIV) are the two commercially available vaccines for prevention of seasonal influenza. Both vaccines contain influenza A subtypes H3N2 and H1N1 and influenza B virus, which are initially grown in hens’ eggs.
  • image Antiviral drugs for prophylaxis of influenza should be considered adjuncts to vaccine and are not replacements for annual vaccination.
  • image The sooner the antiviral drugs are started after the onset of illness, the more effective they are.
  • imageOseltamivir and zanamivir are neuraminidase inhibitors that have activity against both influenza A and influenza B viruses, while the adamantanes have activity against only some influenza A H1N1 viruses. Antiinfluenza agents are most effective if started within 48 hours of the onset of illness.

On completion of the chapter, the reader will be able to:

  1. Differentiate between influenza A and influenza B.

  2. List the primary subtypes of influenza A that are currently circulating.

  3. Differentiate between antigenic drift and antigenic shift.

  4. Identify the virus characteristics necessary for a pandemic.

  5. Discuss the transmission of the influenza virus.

  6. Evaluate the infectivity of adults and children with influenza infection.

  7. List the signs and symptoms of influenza illness.

  8. Describe the diagnostic tests available for influenza.

  9. Differentiate the populations at high risk for complications or severe influenza infection from the general population.

  10. Compare and contrast the trivalent influenza vaccine (TIV) and the live-attenuated influenza vaccine (LAIV), and the different formulations available.

  11. Discuss the emergence of variant influenza A H3N2 and treatment and prevention recommendations for this virus.

  12. Discuss options available for prevention of influenza infection.

  13. Compare and contrast the antiviral agents available for prophylaxis and treatment of influenza.

  14. Formulate a postexposure prophylaxis plan given patient-specific data.

  15. Recommend an appropriate treatment regimen for influenza ...

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