Influenza: evolving strategies in treatment and prevention

Influenza A and B are important causes of respiratory illness in all age groups. Influenza causes seasonal outbreaks globally, and (rarely) pandemics. In the United States, seasonal influenza epidemics account for > 200,000 hospitalizations and > 30,000 deaths annually. More than 90% of deaths are in the elderly. The toll is considerably higher during pandemics. Clinical features of influenza infection overlap with other respiratory pathogens (particularly viruses). The diagnosis is often delayed due to low suspicion and the limited use of specific diagnostic tests. Rapid diagnostic tests are widely available and allow detection of influenza antigen in respiratory secretions within 1 hour; however, sensitivity ranges from 40 to 80%. Currently, four drugs are available to treat or prevent influenza. These include the adamantanes (i.e., amantadine and rimantadine) and the neuraminidase inhibitors (i.e., oseltamivir and zanamivir). Adamantanes are active against influenza A but not influenza B. However, recent emergence of adamantane resistance has rendered these agents ineffective. Hence, adamantanes are not currently recommended in the United States. The neuraminidase inhibitors (NAIs) are effective in treating influenza A or B, and for prophylaxis in selected adults and children. Resistance to NAIs is rare, but influenza strains resistant to oseltamivir have been detected. Vaccines are the cornerstone of influenza control. Currently, trivalent inactivated vaccine (TIV) and live attenuated influenza vaccine (LAIV) are available. These agents reduce mortality and morbidity in high-risk patients (i.e., the elderly or patients with comorbidities), and expanding the use of vaccines to healthy children and adults reduces the incidence of influenza, pneumonia, and hospitalizations due to respiratory illnesses in the community.