- Influenza viruses cause an acute, self-limited febrile illness with myalgias, cough, and malaise. The virus is readily transmissible and associated with outbreaks of varying severity during the winter months.
- Clinical sequelae of influenza virus infection include viral pneumonia and secondary bacterial pneumonia.
- H5N1 avian influenza is transmitted to humans via close contact with infected birds and can cause severe pneumonia and acute respiratory distress syndrome with a case-fatality ratio >50%.
- This condition is most commonly diagnosed clinically, with confirmation by nasopharyngeal swab for rapid antigen testing or direct fluorescent antibody test and culture.
Treatment must be initiated within 48 hours of the onset of symptoms to be effective in immunocompetent patients. Available antiviral treatment regimens are as follows:
- The neuraminidase inhibitors are used in treatment and prophylaxis of influenza A and B.
- Oseltamavir, 75 mg PO bid for 5 days, is well tolerated in capsule and elixir formulations.
- Zanamivir, 10 mg inhaled twice a day for 5 days, is an inhalational agent that may occasionally cause bronchospasm in patients with asthma.
- Amantadine and rimantadine, each 100 mg PO bid, are effective for the treatment and prophylaxis of some influenza A strains; however high levels of
- resistance emerged in H3N2 isolates in 2005, and thus these agents are NOT recommended for seasonal influenza.
- Annual influenza vaccination is recommended for all adults >50 years old and persons with comorbidities. Vaccination has been shown to reduce all-cause mortality in elderly populations.15 Vaccination of high-risk inpatients should be considered during influenza season if there is no underlying febrile illness.