Influenza

Definition

Influenza virus inf causes an acute, self-limited febrile illness with myalgia, cough, and malaise. The virus is readily transmissible and associated with outbreaks of varying severity during the winter months.

Dx

Clinical during flu season, with confirmation of nasopharyngeal swab for rapid antigen testing, PCR, or direct fluorescent antibody test and culture.

Tx

• • Tx is ASx. Antivirals may shorten the duration of illness but must be initiated within 24-48 hours of the onset of sx to be effective in immunocompetent patients.

  • Neuraminidase inhibitors (oseltamivir, 75 mg PO bid or zanamivir, 10 mg IH bid; each for 5 days) are used in tx and prophylaxis of influenza A and B.

  • Adamantanes (amantidine and rimantidine, each 100 mg PO bid) are not effective for the treatment and prophylaxis of influenza B.

  • Circulating strains change annually with varying resistance patterns to both classes of antivirals. Treatment decision must be based on annual resistance data, usually available from the CDC.

  • Vaccination is most reliable prevention strategy. Annual vaccination is recommended for all children aged 6 months to 18 years, and for any adult who wants to avoid influenza infection.

  • Adults >50 years, women who are or will be pregnant during influenza season, and anyone with underlying medical conditions are specifically encouraged to be vaccinated, as are their contacts, including health care workers.

Complications of influenza infection include viral pneumonia and secondary bacterial pneumonia. Viral antigenic drift and shift can cause emergence of strains with enhanced virulence or the potential for pandemic spread, requiring modified therapy or heightened infection control measures.