Update on Prevention and Treatment of Influenza in the Elderly
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INTRODUCTION
Influenza, a lower respiratory tract infection caused by influenza viruses infecting ciliated cells, is associated with up to 300,000 hospitalizations annually in the United States.1 The disease occurs in epidemics in both hemispheres during winter months, but summertime outbreaks do exist.2 Persons with chronic illness and those in long-term care (LTC) settings are at increased risk for complications, including secondary pneumonia.3 Influenza and pneumonia consistently rank as a leading cause of death, of which about 90% of victims are over 64 years old.4 Fatality rates from influenza in nursing homes are the highest, reported from 14%5 to 55%.6,7
In addition to primary influenza viral pneumonia or secondary bacterial pneumonia and death, frail older people are at risk of functional decline after acute influenza. Influenza can exacerbate underlying medical conditions (eg, pulmonary or cardiac disease). Concerns for less common complications, such as myositis, myocarditis, and Guillain-Barré syndrome, can be answered by experts at the Clinician Information Line of the Centers for Disease Control and Prevention (CDC) (877-554-4625). The hotline is available 24 hours a day, 7 days a week, and is staffed by registered nurses with access to the latest CDC guidelines and information. Recent review articles provide further background for the interested reader.8,9
EPIDEMIOLOGY
Influenza activity records from October 2005 to May 200610 reveal:
• Influenza B viruses predominated in Europe
• Influenza A (H1N1) and influenza B predominated in Asia
• Influenza A (H3N2) predominated overall in the United States, with approximately 75% of isolates antigenically matched to the H3N2 component of the 2005-2006 vaccine
• Influenza B activity was more common late in season in the United States, but only approximately 20% of isolates matched the vaccine antigens
• Influenza activity in the United States peaked in early March, but the number of pneumonia and influenza deaths did not achieve the epidemic level
MAKING THE DIAGNOSIS
The diagnosis of influenza is usually presumptive, based on history consistent with influenza symptoms and knowledge of its presence in a community or facility. Though the clinical presentation of influenza in vaccinated elderly persons may be attenuated, individual symptoms and signs are of some value11 (Table I).
• In patients age 60 years or older, the combination of fever, cough, and acute onset increased the likelihood of influenza to the greatest degree (likelihood ratio [LR] = 5.4). The presence of sneezing among older patients made influenza less likely.12
• Rapid diagnostic tests can yield results within a clinically relevant timeframe of 30 minutes to confirm a diagnosis of influenza A or B.13 Tables II and III show comparisons of commonly available tests. (Sensitivities approximately 60-80% and specificities 90-99%.)
• The virus culture remains the reference standard for diagnosis of influenza.
• In high-risk adults, testing is more cost-effective than empiric treatment with neuraminidase inhibitors only when risk of influenza is between 20% and 40%.14
Both rapid and reference tests should be used on the index or other early cases to confirm the type and to verify that the strain is well matched by the vaccine. Treatment of early cases should not be delayed until results of the reference lab are available. If the results are consistent, then subsequent cases in a community or facility may be assumed to have similar pathogens and should be treated accordingly (see below).
PREVENTION OF INFLUENZA
Primary prevention is best accomplished by widespread compliance with vaccination programs.
REFERENCES
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3. Menec VH, MacWilliam L, Aoki FY. Hospitalizations and deaths due to respiratory illnesses during influenza seasons: A comparison of community residents, senior housing residents, and nursing home residents. J Gerontol A Biol Sci Med Sci 2002;57(10):M629-M635.
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J Am Geriatr Soc 2003;51(6):761-767.
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