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Why the Flu Is Often Missed in Older Adults

And why that can result in a much more serious illness

By Leslie Kernisan, MD

(A longer version of this article appeared previously on

Credit: Adobe Stock

You’ve likely heard the news: the flu is pretty bad this year, with the Centers for Disease Control (CDC) confirming a higher-than-usual level of illnesses, hospitalizations and even deaths.

You also probably know that people 65 and older (and certain other groups of people) have a higher risk of falling very ill from the flu and have the highest death rates from flu.

But what you may not know is this: influenza is easily — and often — missed in adults 65 and older.

What do I mean by missed?

  • Older adults or their family members may not realize an older person has the flu, because many older people don’t develop “typical” influenza symptoms.
  • Health professionals often fail to test older people for influenza, even when they are sick enough to be hospitalized. This phenomenon was confirmed in a recently published study.

This is a very serious issue, especially when the flu virus is causing a lot of severe illness, as it is now.

Missing Out on Anti-Influenza Drugs

The main problem is this: delayed, or entirely missed, recognition of influenza means that older adults often don’t get treated early — or at all — with anti-influenza drugs such as oseltamivir (brand name Tamiflu).

Those older adults who have chronic illnesses (especially those affecting the heart or lungs) or are frail don’t want to miss that chance to take anti-influenza drugs. They can’t guarantee an older person will avoid a hospitalization or death from influenza, but they do improve one’s chances.

And anti-influenza drugs are most likely to work when they are given within 48 hours of a person falling ill from influenza, with earlier being better.

So when flu activity is widespread, families need to be prepared to recognize potential flu. And you (and your parents) should be prepared for the possibility that health providers might not think to test for influenza unless asked about it.

If you have not yet been vaccinated for the flu this season, it’s not too late. The flu is often active well into the spring (March, April, or even sometimes May). Older adults will probably get better protection from the vaccine if they get the high-dose flu shot. Use to find a flu vaccine near you.

Usual Symptoms of Influenza

Here’s how the CDC defines “influenza-like illness”:

  • Fever, meaning a temperature of 100°F (37.8°C) or greater, and
  • Cough and/or sore throat, and
  • No other known cause for the symptoms

It’s important to realize that these symptoms on their own are “non-specific,” meaning they can easily be caused by an illness other than influenza (such as a bad cold virus, strep throat or even a bacterial pneumonia).

For this reason, health providers may decide to test a person for influenza, especially if the test result might affect the decision to treat with anti-viral medication or might help contain an outbreak.

“Uncomplicated” influenza is also often associated with other symptoms. The most common ones are nasal congestion and body aches.

Symptoms of Influenza in Older Adults

Many older adults do develop typical symptoms when they fall ill from influenza. But it’s also quite common for them to be sick from the flu and not have a fever, cough or sore throat.

Instead, older adults with the flu often experience the following problems due to influenza:

  1. Common non-specific signs of illness in aging adults. These include symptoms such as:
  • Weakness
  • Dizziness (feeling weak or getting light-headed when standing)
  • Loss of appetite
  • Confusion or worse-than-usual mental function (this is called delirium)
  • Malaise (feeling "blah" or unwell)
  1. An exacerbation (meaning a worsening) of a chronic heart or lung condition. Examples include:
  • An exacerbation of chronic obstructive pulmonary disease, which often means increased shortness of breath, wheezing and/or increased sputum production
  • An episode of worsening heart failure, which often means shortness of breath and/or increased leg swelling
  • A worsening of asthma symptoms

In a recently published study on influenza testing in older adults during flu season, researchers independently tested all adults hospitalized with any type of respiratory diagnosis or shortness of breath for influenza.


“Among patients with study-confirmed influenza, ‘influenza-like illness’ was also less common in older patients,” affecting 74 percent of those at or older than 65 years, 83 percent of those 50 to 64; and 81 percent of those 18 to 49, the study found.

In other words, in this real-world study, 26 percent of hospitalized older adults with proven influenza did not have the typical “influenza-like illness” symptoms of fever plus cough or sore throat.

Why Older Adults May Not Show Typical Flu Symptoms

Here’s a core concept in geriatrics: as people age, they become less likely to have “typical” symptoms when they develop infections and some other types of illnesses.

This is due to two common issues that come up as people age: the aging of the immune system and decreased “physiologic reserve.”

Aging of the immune system Aging is known to eventually bring on changes to the immune system. Since many common symptoms of illness actually reflect the immune system’s response to an infection, a less vigorous immune system will tend to generate less prominent symptoms.

For instance, fever is a very classic sign that the immune system is at work fighting infection. However, studies have found that older adults are less likely to have fever when they are ill with influenza.

Decreased “physiologic reserve” The human body is designed to maintain stability and the ability to carry out key functions, even in the presence of stress or illness. This is why even if one is sick, one can usually stand up and think straight. Key organs keep functioning adequately.

At its peak resilience and effectiveness (usually when you’re in your mid-20s), the body has lots of capacity to effectively respond to stressors.  This is called having a lot of “physiologic reserve.” So although it’s possible for a young person to become delirious — or unable to stand — due to illness, it usually takes a very severe illness to do this.

But as we get older, most organs develop some wear or damage, due to aging or chronic diseases. They don’t have quite as much extra capacity as they used to. So all those systems for maintaining stability and function in the face of illness become less effective.

Special CDC Advisory to Doctors

Since we’re in the midst of a particularly bad flu year, this past December the CDC issued a special health advisory on the diagnosis and treatment of influenza. (You can read it here.)

It tells doctors that "influenza should be high on their list of possible diagnoses for ill patients" and advises them to start treating all high-risk patients (including people 65 and older) with suspected flu right away. "Antiviral treatment should be started as soon as possible after illness onset and should not be delayed even for a few hours to wait for the results of testing," the advisory said.

Taking Action

To summarize: When the flu is widespread, clinicians and families should be quick to suspect that a sick older person might have the flu, even if he or she doesn’t have a fever, a cough, a sore throat, body aches or any of the other “typical” flu symptoms.

In an older person, feeling weak or confused may be the only sign of having the flu.

Be proactive about asking for influenza testing and anti-virals while any test results are pending. But I’ll be honest with you: you may have to be persistent, especially if the doctor waves off your concern or questions about influenza.

With the help of informed and proactive families, we can help more older adults get the care they need, and so reduce serious illnesses and deaths from the flu.

Leslie Kernisan, MD
Leslie Kernisan, MD, is a practicing geriatrician in San Francisco who believes that it shouldn’t be so hard for older adults and families to get the right kind of help with health concerns. She's the author of When Your Aging Parent Needs Help and the founder of the website and podcast Better Health While Aging and the Helping Older Parents online programs. Read More
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