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Influenza causes significant morbidity and mortality, particularly among young children and the elderly. Seasonal influenza epidemics result in 25 to 50 million influenza cases, approximately 200,000 hospitalizations, and more than 30,000 deaths each year in the United States.1-3 Influenza infection can occur at any time during the year with the highest rates of illness occurring between December and March.4 Influenza A and B are the two types of influenza viruses that cause disease in humans. Influenza A viruses are categorized into different subtypes based upon presence of two surface antigens—hemagglutinin and neuraminidase.1-2Immunity to influenza virus occurs as a result of the development of antibody directed at the surface antigens.

The route of influenza transmission is person-to-person via inhalation of respiratory droplets. The incubation period for influenza ranges between 1 and 4 days, with an average of 2 days.1,4-5 Classic signs and symptoms of influenza include rapid onset of fever, myalgia, headache, malaise, nonproductive cough, sore throat, and rhinitis. Signs and symptoms typically resolve in 3 to 7 days; however, cough and malaise may persist for more than 2 weeks. Nausea, vomiting, and otitis media are commonly reported in children. The gold standard for the diagnosis of influenza is viral culture. The clinical utility of the viral culture is limited because of the length of time to receive results. Tests such as the rapid antigen and point-of-care (POC) tests, direct fluorescence antibody (DFA) test, and the reverse transcriptasepolymerase chain reaction (RT-PCR) assay may be used for rapid detection of the influenza virus.2

Annual vaccination is the most effective prevention of influenza. Vaccination should be administered to any person who wishes to reduce the likelihood of becoming ill with influenza or transmitting influenza to others.1-2 Emphasis should be placed upon vaccinating certain groups at higher risk of influenza infection and influenza related complications (Table 30-1). The trivalent influenza vaccine and the live-attenuated influenza vaccine are the commercially available vaccines. Both vaccines are grown in hens eggs, are trivalent, and contain equivalent strains (influenza A H1N1, influenza A H3N2, and influenza B).1,6-8 See Table 30-2 for a comparison of influenza vaccines.

TABLE 30-1 Target Groups for Vaccination and Persons at High Risk of Influenza Complications1

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