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January 31, 2018 -- Older adults always get hit hard with flu, with up to 85% of flu deaths usually happening in those age 65 and older, the CDC says.

Yet doctors are less likely to order a flu test for adults in that age group, and they could miss diagnosing the flu, new research finds.

Flu symptoms in older adults can differ from those of younger people, says Keipp Talbot, MD, associate professor of infectious diseases at Vanderbilt University School of Medicine. She is the senior author of the new study, published online in the Journal of the American Geriatrics Society. "Not everyone who has flu has a fever, especially those over age 65," she says.

Doctors don’t always use a flu test because they can make a diagnosis based on a patient’s symptoms. The study suggests testing may be more helpful in older adults since their symptoms can be nontypical.

Missing a flu diagnosis can be especially dangerous in older adults, as they are more likely to get complications from the flu than younger people. Up to 75% of flu hospitalizations are in that older age group. Antiviral drugs that can make the flu less severe should be given within 2 days of the start of symptoms.

Flu Study Details

Talbot's team looked at the records of more than 1,400 adults, ages 18 and older, treated in four different hospitals from November 2006 through April, 2012, with either a respiratory illness or fever.

The researchers took nose and throat swabs of the patients enrolled in the study. They then did the RT-PCR flu test, which looks at genetic material in the virus and is more accurate than the rapid influenza test.

They confirmed that 136 patients had the flu. Only 59 of the 136, or 43%, had been tested by their doctors, even though they sought medical care and reported symptoms.

Among the other findings:

  • Older patients were less likely than younger ones to report fever, cough, and sore throat, the usual definition of flu-like illness that would trigger testing. Fewer than half of older adults reported these usual symptoms.  
  • The presence of a fever seemed to play a role in whether the doctors ordered testing. Of those tested, 73% had a fever. Of those not tested, just 44% did.
  • Younger patients were more likely to be tested than older ones.
  • Overall, only 28% of the patients' doctors ordered flu tests.
  • Doctors at the one academic hospital studied were twice as likely to order a flu test for patients than those at the three community hospitals.
  • Fewer than 3% of older patients who had a respiratory illness got antiviral drugs, and only 11% of those who had the flu confirmed by the RT-PCR test did.

Flu Symptoms in Older Adults

While some older adults do report the typical flu symptoms, not all do, Talbot says. "Very often, older adults (with the flu) don't get a high fever," she says.

Also, their main symptoms may be a slight loss of appetite and fatigue, says Lona Mody, MD, the Amanda Sanford Hickey professor of internal medicine at the University of Michigan.

Other symptoms in older adults may be cough, shortness of breath, muscle aches, lower-grade fevers, and weakness, says Amesh Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security.

The findings are important because doctors know that the aging immune system cannot fight off the flu as well as when people are younger, Talbot says. "As we age, so does our immune system," she says.

Adalja, who's also a spokesman for the Infectious Diseases Society of America, says the new study shows that flu testing needs to be improved.

"I have a low threshold for testing people for influenza, even if they don’t meet the classic definition of flu [symptoms]," he says.

Testing is especially important in hospitalized patients, as the flu can spread quickly in hospitals.

Adalja says he prefers the molecular diagnostic testing for accuracy.

But the rapid testing is often done instead because it is cheaper and faster, Talbot says.

Preventing the Flu in Older Adults

Two flu vaccines are specially licensed for older adults, Talbot says. The ''high dose'' contains 4 times the amount of active ingredient as the regular flu shot and causes a stronger immune response

However, if those two vaccines are not available, getting the regular flu vaccine is better than waiting for the high dose or adjuvant, experts say.

What about getting a ''booster" of the flu vaccine? Not a good idea, Talbot says. "We don't understand how the immune system responds to multiple vaccines," she says. "I would not recommend a second vaccine, because there is not data to support its use as safe and effective."

Besides getting the flu vaccine each year before November (some doctors suggest September or October is even better), Talbot advises older adults to get vaccinated against pneumonia, which can be a serious complication of the flu.

When to Seek Help

Some older adults do have the classic symptoms of cough, fever, and sore throat, Talbot says. Seek help if you have those or:

  • Difficulty breathing
  • Coughing up phlegm
  • Difficulty taking care of yourself

"If you are worried, it's always appropriate to seek medical care," she says.

And if your doctor doesn't suggest a flu test? Speak up, Mody says. She suggests simply asking: "Can you check me for flu?" If your family members, co-workers, or neighbors have had the flu recently, tell your doctor that, too, she says.


Talbot reports research funding from Sanofi Pasteur, MedImmune and Gilead; she has been an advisor for VaxInnate and Seqirus. Adalja reports serving as a consultant for Roche Diagnostics. Mody has no relevant disclosures.

Show Sources

Keipp Talbot, MD, associate professor of infectious diseases, Vanderbilt University School of Medicine, Nashville.

Journal of the American Geriatrics Society: "Underdiagnosis of influenza virus infection in hospitalized older adults."

Amesh Adalja, MD, senior scholar, Johns Hopkins Center for Health Security, and spokesman, Infectious Diseases Society of America.

Lona Mody, MD, Amanda Sanford Hickey professor of internal medicine, University of Michigan, Ann Arbor.

CDC: "Diagnosing Flu," "What You Should Know and Do this Flu Season If You Are 65 and Older."

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