Flu Can Be Catastrophic in Older Patients: 5 Things to Know

Not everyone experiences the same effects from influenza. Adults aged 65 years or older suffer the most severe health effects, accounting for approximately 90% of influenza-related deaths and 50%–70% of hospitalizations. They also have an increased likelihood of suffering long-term sequelae, including persistent loss of function and disability.

Prepare yourself for the upcoming flu season with these five things to know about influenza in older patients.

1. Advanced age and chronic conditions expose seniors to different risks.

Seniors commonly have chronic medical conditions, such as heart disease, diabetes, or respiratory diseases, such as chronic obstructive pulmonary disease or asthma, which contribute to an increased risk for complications. In addition, age-related dysfunctions of the immune system contribute to disease severity and poorer response to standard vaccines. Frailty is a significant indicator of increased risk for poor outcomes and should be taken into consideration in management.

There are direct and indirect effects from influenza. Direct effects of influenza include exacerbations of existing conditions, as well as additional problems, such as bronchitis and pneumonia. Indirect effects include triggering cardiovascular events, such as heart attack and stroke. Influenza can also exacerbate renal disorders, heart failure, and diabetes and trigger delirium that may lead to functional decline, falls, and fractures.

The risk for influenza-related mortality is five times higher among people with heart disease, 12 times higher among those with chronic lung disease, and 20 times higher among those with both heart and lung disease.

Risks in older vs younger seniors differ as well. Research shows significant stepwise increases in the population rates of influenza hospitalization with each 10-year increase in age. Hospitalization rates among adults aged 85 years and older are two to six times greater than rates for adults aged 65 to 74 years.

2. The immune system becomes dysfunctional with age.

The immune system becomes weaker and dysregulated with age. According to Melissa Andrew, MD, associate professor at Dalhousie University, Nova Scotia, Canada, humoral immunity tends to decline, and the antibodies produced may be less effective.

Multiple chronic medical conditions with underlying components of inflammation have additional effects, referred to as "inflammaging." Conditions such as diabetes, arthritis, and cardiovascular disease create a low-grade, chronic, systemic proinflammatory state with elevated levels of proinflammatory cytokines. Along with this constant assault is a consequent degeneration of tissue.

The immune system has an anti-inflammatory mechanism to keep things in balance and limit damage from inflammatory responses. But in older adults, this homeostasis is dysregulated; problems include thymic atrophy and diminished T-cell activity. All in all, with an infection such as influenza, the immune system doesn't mount an immune response that is as effective as in younger adults.

3. Influenza may present differently in older adults.

Older patients often present with complaints of general malaise and nonspecific symptoms that can lead to a missed diagnosis of influenza. Because influenza often exacerbates existing chronic conditions, those conditions may be considered the primary diagnosis, and influenza can go unrecognized, said Andrew.

Seniors commonly present with fever and cough, but this isn't always the case. A study of patients aged 60 and older who presented with influenza-like illness (ILI) in acute care hospital emergency departments found that only 31% of the patients with confirmed influenza met the Centers for Disease Control and Prevention criteria for ILI (temperature ≥37.8 °C and cough and/or sore throat). Researchers concluded that "current influenza-like illness definitions did not always help detect influenza in older adults." Confusion was also often associated with influenza, as was wheezing.

Another study found that even when older patients presented with fever and ILI, healthcare professionals were less likely to order tests for influenza; older patients were tested at significantly lower rates than younger patients.

4. Influenza can lead to catastrophic disability.

Influenza is often considered to be associated with short-term morbidity, but many seniors experience functional decline that persists. About 1 in 5 or 6 older adults hospitalized for influenza end up with persistent functional decline, and many never return to their baseline status before getting influenza.

"Persistent loss of function, or catastrophic disability, should be considered when looking at the overall burden of flu," said Andrew. Catastrophic disability can be measured using the Barthel Index, which measures 10 activities of daily living.

Loss of the ability to perform two or more daily activities represents catastrophic functional decline, which can include losing the ability to get dressed, walk around, or bathe. Higher-order functions, such as making a meal or going out to buy groceries, are even more likely to be affected by acute illness. Close to 15% of older adults hospitalized with influenza experience catastrophic disability, Andrew said. The Clinical Frailty Scale is another tool that can be used in this population.

Measures of frailty can be used to determine who is most at risk of losing function. It is a continuum, ranging from resilient and fit to vulnerable. Resilient patients recover well from flu, but frail patients often end up with greater disability.

The Serious Outcomes Surveillance (SOS) Network found that mortality rates vary by the level of frailty in patients. According to SOS data for 2017–2018, for people with moderate or severe frailty, the mortality rate is 12%, whereas for those who are less frail, mortality is 2%, said Andrew. This gradient is true of younger frail patients too, not just those aged 65 or older.

5. Some vaccines are designed specifically for seniors.

Owing to the high risks older adults face from influenza, prevention with vaccination is the best strategy. The CDC advises that people in this age group receive the influenza vaccine with an approved product. Standard-dose, unadjuvanted influenza vaccines have been available the longest, but high-dose, adjuvanted or recombinant vaccines are also available.

The newer HD-IIV3 (Fluzone High-Dose), RIV4 (Flublok Quadrivalent), and aIIV3 (Fluad adjuvanted) are more immunogenic in older adults than standard-dose and unadjuvanted vaccines, but data are very limited for direct comparisons. As a result, the CDC does not recommend one over the other.

Pippa Wysong is a freelance medical and science writer with over 30 years of experience writing for both medical and popular audiences. She is a former staffer at The Medical Post, and has written numerous projects for Medscape.

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