Influenza [IDSA]

Key Points ÎÎInfluenza illness is caused by infection with one of three types of circulating RNA viruses: influenza A, B, or C virus. Influenza C virus infection causes respiratory illness that is generally milder than for influenza A and B virus infections and for which diagnosis, treatment, and prevention are generally not pursued. ÎÎDuring influenza season, influenza viruses circulate ubiquitously in the population. Each year, between 5% and 20% of the population is infected with influenza viruses, and an estimated annual average of 36,000 deaths and over 200,000 hospitalizations attributable to influenza virus infection occur in the United States. ÎÎThe elderly, the very young, and persons with underlying medical conditions such as those with cardiopulmonary disease, diabetes, immunocompromised persons, and pregnant women are at increased risk for severe disease or death secondary to influenza virus infection. ÎÎAppropriate use of diagnostic testing, along with timely administration of antiviral medications, may improve clinical outcomes of influenza virus infection, may reduce other unnecessary diagnostic testing, may decrease duration of required medical care, and may reduce both appropriate (for presumed bacterial complications) and inappropriate use (to prevent bacterial complications) of antibacterial agents. Shedding Time ÎÎImmunocompetent persons: may sometimes be 5 days from onset ÎÎInfants and young children: commonly one week or longer ÎÎImmunocompromised persons: may sometimes be weeks or months Vaccination Contraindications to vaccination include anaphylactic hypersensitivity to eggs or other vaccine components; moderate to severe febrile illness; and as a precaution, a history of Guillain-Barré Syndrome within 6 weeks of a previous influenza vaccination. ÎÎInfluenza vaccination is the primary tool to prevent influenza, and antiviral chemoprophylaxis is not a substitute for influenza vaccination. ÎÎWhenever possible, influenza vaccine should be administered, and vaccination should continue in recommended persons until influenza is no longer in community circulation (B-II). ÎÎWhen one family member develops suspected or confirmed influenza and any other family member is at high risk for complications secondary to infection, including infants less than 6 months of age, all eligible family members should be vaccinated (A-I). ÎÎChildren aged < 9 years who receive inactivated influenza vaccine for the first time require 2 doses of vaccine, with the second dose administered ≥ 4 weeks after the first dose. The immune response peaks 2 weeks after the second dose. ÎÎInfluenza vaccination may have lower effectiveness in persons who are significantly immunocompromised.

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