5 Surprising Signs of an Infection in Older Adults

Don’t overlook these unusual symptoms as flu season approaches

Claire Leibowitz,

AARP

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Published October 16, 2025

Chris Gash

Feeling off but not spiking a fever? That doesn’t necessarily mean you don’t have the flu, COVID or other common illnesses that circulate this time of year.

Many of the early warning signs of common infections appear differently in older adults — and some of the symptoms can be surprising.

Much of it has to do with the weakening of the immune system with age, a process known as immunosenescence. This decline blunts the typical response to fighting off infection and the symptoms that result from this defense, like fever and chills. Instead, common illnesses can appear with less common symptoms.

“We see very atypical presentations for some of these respiratory viruses in older adults,” says Dr. Morgan Katz, an infectious disease specialist at Johns Hopkins Medicine. This is why learning to recognize and monitor these symptoms is key.

For example, any changes in a person’s appetite, personality and overall behavior are worrisome, doctors say, especially when these changes happen quickly.

“Infection is a concern when there’s any rapid change in an older person, meaning overnight or within hours, something is different from how it had been before,” says Dr. Nina Blachman, a geriatrician at New York University Langone. But just because someone is experiencing a symptom like confusion doesn’t necessarily mean they are sick — that’s why knowing a person’s usual state, or baseline, and tracking changes throughout the day is so important.

Staying on top of so-called baseline metrics is also important if you have a separate and unrelated health condition, such as diabetes or heart disease, since a new infection can exacerbate an underlying issue.

Here are five surprising symptoms that could signal you’re getting sick, plus tips on how to stay healthy this cold and flu season.

Unusual symptoms of an infection

1. Confusion

Any new or worsening confusion could be a warning sign of an infection, says Katz. A small study published in the journal Clinical Nursing Research found that infection and dehydration were the leading causes of short-term confusion among residents in a long-term care facility.

Delirium, a more intense type of confusion, can also be a symptom of infection. “Often, it’s a very concerning sign of a more severe infection,” says Dr. Camille Vaughan, division director of geriatrics at the Emory University School of Medicine. Still, she says, experts “don’t know all of the pathways that lead to those changes in brain function that lead to that confusion state.”

In a study published in the British Journal of General Practice, researchers interviewed 22 patients and six caretakers and identified a “spectrum” of confusion resulting from infection. Patients described the time of their illness as a “blur,” and others reported feeling muddled or out of control.

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2. Falling

Falls can result from a variety of causes, ranging from medications to changes in vision to underlying health conditions. An infection can also increase a person’s risk of falling, especially when the body is weak or fatigued from fighting off an illness.

“I don’t want to imply every time you have a fall, you need to be thinking about an infection,” says Vaughan. “It could be something where we just want to be a little more tuned-in that day or so afterward, to see if something may be brewing or worsening.”

3. Changes in appetite

Another unusual sign of a respiratory infection is a change in appetite.

“If you see a patient looking different from their baseline in any way — and that can be as simple as refusing breakfast when they typically eat breakfast — that’s when you really start monitoring that patient more frequently,” Katz says.

A 2023 study in Clinical Nutrition ESPEN looked at almost 2,000 participants with reported COVID-19 or other possible infections. It found adults over age 75 reported a lack of appetite more often than those under 35 did. Early detection and management of COVID-19 based on appetite loss could reduce the risk of further complications after infection, the researchers wrote.

4. Fatigue or new weakness

The Clinical Nutrition ESPEN study also found that older adults reported fatigue more than younger age groups did. Similarly, the researchers suggest catching the symptom early on and detecting and treating the illness and could reduce the risk of future complications.

Fatigue is a common symptom of illness in all ages. “[It] may manifest as new weakness or delirium, which, again, is different than our younger counterparts, often because older adults may not be able to describe their symptoms like younger adults could,” Katz says.

New weakness or any deviations from normal “should be a clue that they potentially have an infection,” Blachman adds.

5. A mild fever

“You can’t wait for that fever because it may not actually happen,” Blachman says, “but the patient may be very sick.” That’s because when the immune system weakens, fevers don’t rise as high.

Katz says tracking a person’s temperature can help determine if an older individual is sick. Temperatures 2 degrees Fahrenheit above a person’s normal temperature should be considered a fever.

“It wouldn’t be our typical 100.4 degrees Fahrenheit cutoff that we see in younger individuals,” Katz adds.

Preventing and treating infections

Sometimes, getting sick is inevitable. But during respiratory illness season, it’s crucial to take care of your body so you’re strong enough to fight off whatever comes your way.

“Vaccines are by far the best thing to do,” says Vaughan. “I want to continue to make sure that people, especially in our 65-and-older group, are getting those routine vaccines this fall.”

This year’s COVID-19 booster is available to most individuals after a brief discussion with a health care provider, such as a doctor or pharmacist, and many doctors say it’s especially important for older adults who are more likely to experience complications from COVID. Older adults should also get a high-dose flu shot, and an RSV vaccine is recommended for people 75 and older and for some people ages 50 to 74.

“Other things to think about are just getting enough sleep, staying hydrated, eating a healthy diet and exercising. All of those things can keep people well,” Blachman says.

If you do find yourself with some atypical infection symptoms, Katz recommends checking your temperature and pulse oximetry (the levels of oxygen in the blood) roughly every two hours to gauge whether your body is going in the wrong direction.

Testing to see what’s causing your symptoms, either at home or at the doctor’s office, is important too, since there are antiviral treatments for illnesses like flu and COVID, and they work better the sooner you start them.

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