Flu can cause life-threatening complications for vulnerable populations — here are the warning signs

The 2019-20 flu season is expected to be one of the worst in a decade, according to the National Institute of Allergies and Infectious Diseases.

While much attention has been focused on the coronavirus, the flu continues to be a major threat.

Since October 2019, between 19 million and 26 million people have been infected with influenza. Between 8.6 million and 12 million people with the flu have visited a doctor and 10,000-25,000 people have died across the U.S.

The data was collected by the CDC from Oct. 1, 2019, through Jan. 25, 2020. Each range is an estimate, according to the agency, because it cannot capture all cases of the flu in the U.S.

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The CDC warns that the most vulnerable populations are people age 65 and older, pregnant women, people of any age with chronic medical conditions such as asthma, diabetes and heart disease, and children under age 5.

The flu can often be confused for a common cold, but influenza symptoms include a fever or chills, cough, sore throat, runny nose, body aches, headaches and fatigue. It’s also common for children to experience vomiting or diarrhea.

The flu can cause mild to severe illness, and while most people recover within a few days to two weeks, vulnerable populations can end up with complications.

Here are some minor to severe complications that can result from the flu:

  • Sinus or ear infection
  • Inflammation of the heart
  • Brain swelling
  • Muscle or tissue swelling
  • Multi-organ failure
  • Pneumonia
  • Sepsis

According to the CDC, some of the more serious complications can result from the flu virus alone or from infections of the virus and other bacteria. If the flu virus ends up in a person’s respiratory tract, it can trigger “an extreme inflammatory response in the body,” which can lead to sepsis. Sepsis is the body’s response to an infection getting into the bloodstream.

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The flu can also cause chronic problems, such as asthma or diabetes, to be worse for some people, triggering flare-ups. Those with chronic heart disease may also see the condition worsen because of influenza.

People with a higher risk of life-threatening complications should be mindful of the following warning signs:


  • Fast breathing or difficulty breathing
  • Bluish tint to the lips or face
  • Ribs going in with each breath
  • Chest pain
  • Severe muscle pain or a child refusing to move around
  • Dehydration (dry mouth, no tears when a child cries or no trips to the bathroom for 8 hours)
  • Seizures
  • Fever above 104 degrees Fahrenheit
  • Any sign of a fever in a child less than 12 weeks old
  • Fevers or cough that improve but then come back or worsen
  • Chronic medical conditions that worsen because of the illness


  • Difficulty breathing or shortness of breath
  • Pain or pressure in the chest or abdomen
  • Constant dizziness, confusion or inability to wake up
  • Seizures
  • Not urinating
  • Severe muscle aches
  • Weakness or unsteadiness
  • Fever or coughs that improve and then come back or worsen
  • Chronic medical conditions that worsen because of the illness

The CDC also urges people to speak with a medical professional for any symptoms - even if they’re not on the list - that are concerning.