Influenza

SOURCE

Source: Njoku JC. Influenza. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146071550. Accessed March 25, 2017.

DEFINITION

• Viral illness associated with high mortality and hospitalization rates in persons >65 years, children under 2 years old, and those who have underlying medical conditions.

ETIOLOGY

• Transmitted person to person via inhalation of respiratory droplets.

PATHOGENESIS

• Hemagglutinin allows virus to enter host cells.

• Incubation period: 1–7 days (average 2 days)

  • Children infectious for longer period of time than adults.

  • Viral shedding persists for weeks to months if immunocompromised.

• Immunity occurs through antibody development directed at surface antigens, particularly hemagglutinin.

  • Immunity to one subtype does not confer protection against other subtypes or types.

EPIDEMIOLOGY

• Seasonal epidemics result in 25–50 million cases, ~200,000 hospitalizations, and >30,000 deaths each year in the United States.

  • Overall, more people die of influenza than of any other vaccine-preventable illness.

  • Deaths often result from.

    • Secondary bacterial pneumonia.

    • Primary viral pneumonia.

    • Exacerbations of underlying comorbidities.

• Types A, B, and C affect many species.

  • A and B viruses cause disease in humans.

PREVENTION

• Primary prevention.

  • Vaccination primary means of influenza prevention.

  • Infection control measures to limit spread of influenza.

    • Hand hygiene.

    • Basic respiratory etiquette (cover your mouth when coughing and throw soiled tissues away)

    • Contact avoidance.

  • Annual vaccination recommended for all persons age 6 months or older.

  • Two vaccines currently available (Tables 1 and 2)

    • Trivalent influenza vaccine (TIV)

      • Intramuscular product approved for use in persons age 6 months or older.

    • Live-attenuated influenza vaccine (LAIV)

      • Intranasal product approved for use in healthy people 2–49 years of age.

      • Not indicated for use in pregnant women or immunocompromised person.

      • Administer 48 hours after completion of influenza antiviral therapy.

      • Administer antiviral therapy 2 weeks after administration of LAIV.

    • Specific strains included in vaccine change each year based on antigenic drift.

• Postexposure prophylaxis.

  • Antiviral drugs available for prophylaxis not replacements for annual vaccination (Table 3)

  • Consider prophylaxis for persons at high risk of serious illness and/or complications who.

    • Cannot be vaccinated.

    • Are vaccinated after influenza activity has begun in their community because development of sufficient antibody titers after vaccination takes ~2 weeks.

    • Are unvaccinated and have frequent contact with those at high risk.

    • Have an inadequate response to vaccination (eg, advanced HIV disease)

    • Reside in long-term care facility during influenza outbreak (regardless of vaccination status)

    • Are unvaccinated and household contacts of someone diagnosed with influenza.