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This chapter addresses the following Geriatric Fellowship Curriculum Milestone: #18

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LEARNING OBJECTIVES

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Learning Objectives

  • To understand the biology of influenza virus that leads to “drift” and “shift” in surface protein structure and their impact on vaccine formulation and the emergence of influenza pandemics.

  • Recognize clinical situations where there is a need for diagnostic testing to confirm a specific viral etiology (influenza or respiratory syncytial virus [RSV]) in symptomatic older adults and recommend the specific tests appropriate in different clinical scenarios.

  • Identify appropriate interventions to control outbreaks of influenza or RSV in a nursing home.

  • Recognize the appropriate use of antiviral therapies for influenza in seniors.

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Key Clinical Points

  1. The influenza virus has a segmented RNA core that encode key proteins on the viral surface including hemagglutinin and neuraminidase. Annual mutations in the RNA lead to “drift” in these proteins requiring annual reformulation and administration of the vaccine.

  2. When entire segments of the influenza RNA recombine in animals, it can lead to an antigenic “shift” and result in a pandemic as there may be little or no immunity in the population.

  3. Detection of influenza virus by direct antigen testing is insensitive (as low as 20%) in older adults, and a negative test does not rule out influenza infection. Reverse transcriptase polymerase chain reaction (RT-PCR) is more than 90% sensitive. Similarly, RSV is best detected by RT-PCR.

  4. RSV is clinically indistinguishable from influenza in older adults—both may present subtly or primarily as an exacerbation of underlying chronic illnesses.

  5. Antiviral therapy with neuraminidase inhibitors is indicated for treatment of influenza and as chemoprophylaxis for nursing home outbreaks. Supportive care is currently the only treatment for RSV.

  6. Influenza immunization is recommended for all older adults. A high-dose vaccine is more effective than a standard-dose vaccine in seniors.

  7. Immunization of staff reduces influenza mortality for nursing home residents.

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INFLUENZA

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Viruses are an important threat to the health of older adults. Each year, it is estimated that influenza alone is associated with the death of 36,000 older adults in the United States. Despite immunization, outbreaks of influenza occur regularly in nursing homes and other long-term care facilities. This section of the chapter summarizes the biological, epidemiological, and clinical features of influenza that are relevant to older adults, with a particular emphasis on prevention.

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Clinically Relevant Biologic Characteristics of Influenza Virus

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To properly understand the impact of influenza in older adults, it is important to be familiar with several key characteristics of the virus. The structure of influenza consists of an envelope with a central nucleic acid core comprised of single-stranded RNA that encodes key structural proteins of the virus including hemagglutinin and neuraminidase on the envelope. There are three types of influenza viruses A, B, and C. However only A and B are clinically relevant. Influenza A viruses are characterized by the structure of the hemagglutinin, a surface protein ...

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